Committee of the Privy Council, which consists of the Lord President of the Council, the Lord Chancellor, the Chief Justices, and Chief Baron, the Master of the Rolls, and Lords Justices of the Court of Appeal in Chancery, the Judge of the High Court of Admiralty and of the Court of Probate, and certain other persons nominated by the Crown. In ecclesiastical causes, Bishops who are Privy Councillors are members of the committee. The proceedings of this tribunal, which is a Court of Record, have been regulated by various statutes (3 & 4 Will. IV. c. 41; 6 & 7 Vict. c. 38). The Judicial Committee has authority in various other matters, as to which see PATENTS, S. 2; JUDICIAL COMMITTEE, S. 2. (Blackst. Comm.,' Mr. Kerr's ed., vol. vi. p. 225.) DENIZEN. Letters of Denization are now disused, aliens generally having recourse to the simpler and more advantageous certificate of naturalisation granted by the Secretary of State. [ALIEN, S. 1.]

DENTEX, a genus of Fishes belonging to the Family Sparida. It has the following characters :-Body deep, compressed; dorsal fin, single; head large; teeth conical, placed in a single row, four in the front above and below, elongated, and curved inwards, forming hooks; teeth on the branchial arches, but none on the vomer or palatine bones; nose and suborbital space without scales; branchiostegous rays 6. There are several species of this genus.

D. vulgaris, the Four-Toothed Sparus, is regarded as a native of England. Only one specimen, however, seems to have been taken in this country, and that by Mr. Donovan in 1805 off Hastings. It is a very common fish in the Mediterranean, and is the Dentex of the Romans. It is remarkable for the great length of the four anterior teeth in each jaw. It acquires sometimes a large size weighing from 20 to 30 pounds, and measuring 3 feet in length. Mr. Donovan's specimen weighed 16 pounds. "A more voracious fish," says Mr. Donovan, "is scarcely known; and when we consider its ferocious inclination and the strength of its formidable canine teeth, we must be fully sensible of the great ability it possesses in attacking other fishes even of superior size, with advantage. It is asserted, that when taken in the fisherman's nets, it will seize upon the other fishes taken with it, and mangle them dreadfully. Being a swift swimmer it finds abundant prey, and soon attains to a considerable size. Willughby observes that small fishes of this species are rarely taken, and the same circumstance has been mentioned by later writers. During the winter it prefers deep waters, but in the spring or about May it quits this retreat, and approaches the entrance of great rivers, where it deposits its spawn between the crevices of stones and rocks.

"The fisheries for this kind of Sparus are carried on upon an extensive scale in the warmer parts of Europe. In the æstuaries of Dalmatia and the Levant, the capture of this fish is an object of material consideration, both to the inhabitants generally as a wholesome and palatable food when fresh, and to the mercantile interests of those countries as an article of commerce. They prepare the fish according to ancient custom, by cutting it in pieces and packing it in barrels with vinegar and spices, in which state it will keep perfectly well for twelve months."

DENTINE. [TISSUES, ORGANIC, S. 1.] DEODAND. Juries and judges having (as stated in the 'Penny Cyclopædia,' vol. viii. p. 411) alike condemned this species of forfeiture, the law has been altered by the statute 9 & 10 Vict. c.6 2, and deodands are now entirely abolished. DEPOSITIONS (in Criminal Cases). The statute 11 & 12 Vict. c. 42, has prescribed with great care and exactitude the mode in which the depositions of witnesses are to be taken in criminal cases. The statute requires a deposition to be put in writing, to be read over to the witness, and to be signed by him. Unless these formalities are complied with, and the deposition has been taken in presence of the accused, and he has had full opportunity of cross-examination, it is not admissible in evidence against him.

DEPOSITIONS (in Equity). Evidence is now taken in Chancery by deposition before an officer called an Examiner, not by written interrogatories, but orally, in the presence of the parties, the witness being subject to cross-examination and re-examination. This new system, in imitation of that public examination of witnesses pursued in courts of common law, which is justly considered a great test of truth, was introduced as part of the practice of the Court of Chancery by the stat. 15 & 16 Vict. c. 86. (Blackstone's 'Commentaries,' Mr. Kerr's ed., vol. iii. p. 520.)

DEPPING, GEORGE BERNARD, was born at Münster,

May 11, 1784. Having completed his educational course, he visited Paris in 1803, when, forming acquaintances there, and observing the facilities which the city afforded for the prosecution of literary studies, he determined to make it his permanent residence. The rest of his life was spent there in the uneventful career of a busy littérateur.

A more

For many years M. Depping mainly occupied himself in preparing juvenile and popular works chiefly on geographical subjects, in translating, and in writing for magazines and encyclopædias. His first important original work was one written for a prize offered by the Institute on the Expédition Maritime des Normands en France au Dixième Siècle." It won the prize, was printed in 1826, and revised in 1844: it is a work of sterling value, and contains the fruits of extensive researches in Scandinavian literature. important work, for which this had prepared the way, Was his Histoire de la Normandie,' from the Conqueror to the re-union of Normandy with France (1066 to 1204), 2 vols. 8vo, 1835. Among his other more important works may be named- Histoire du Commerce entre le Levant et l'Europe, depuis les Croisades jusqu'à la Fondation des Colonies d'Amerique,' 2 vols. 8vo, Paris, 1830; 'Les Juifs dans le Moyen Age, Essai Historique sur leur Etat Civil, Commercial, et Littéraire,' 8vo, 1840; Règlements sur les Arts et Métiers, rédigés au Triezième Siècle, et connus sous le nom de Livre des Métiers d'Etienne Boileau,' &c., 4to, 1837; 'Geschichte des Kriegs der Münsterer und Kölner 1672-1674,' Svo, Münster, 1840: Correspondance Administrative sous le Règue de Louis XIV.' (forming vols. i. to iii. of the Collec tion des Documents Inédits de l'Histoire de France'), 4to, 1850-53; 'Romancero Castellano,'1 vol.12mo, Paris, 1817, and, greatly enlarged, 2 vols. 12mo, Leipzig, 1844. Some of the above works have been translated into German and Dutch, while several of his juvenile works have been translated into most of the European languages. M. Depping wrote many of the more important articles in the 'Biographie Universelle,' L'Art de Vérifier les Dates,' &c. He died in Paris, September 5, 1853. DERMATINE. [MINERALOGY, S. 1.]

DESIGN, SCHOOLS OF. [SCIENCE AND ART, DEpartMENT OF, S. 2.]

DESMIDIEÆ, a group of organised beings regarded by some naturalists as Animals and by others as Plants. The botanists who have adopted them into the vegetable kingdom have regarded them as Algae, and allied to the Diatomacea. Some however who admit the vegetable characters of Desmidiea deny them to Diatomacea. Dr. Lindley admits the Desmidieæ as a sub-order of the Diatomacea, which he characterises as crystalline angular fragmentary bodies, brittle, and multiplying by spontaneous separation. Amongst this group of beings the Desmidice are characterised as being cylindrical.' The following is the definition of this family as given by Mr. Ralfs in his British Desmidieæ,' a work which has greatly increased our knowledge of these obscure beings: "Freshwater figured, mucous, and microscopic Algr, of a green colour. Transverse division mostly complete, but in some genera incomplete. Cells or joints of two symmetrical valves, the junction always marked by the division of the endochrome, often also by a constriction. Sporangia formed by the coupling of the cells and union of their contents.' It will be seen from this definition that Mr. Ralfs regards these beings as plants. The principal points on which he relies for establishing this position are the occur rence of conjugation and swarming, and the presence of starch amongst the Desmidica.

The occurrence of a union or conjugation of the two filaments for the production of spores, has long been known amongst certain forms of Conferva. This has been seen by many observers to occur amongst the Desmidien. In the Euastrum rupestre (fig. 3 represents the genus) Nägeli describes this process. Two individuals are placed close together, and push out short processes, which meet, and by the absorption of the wall constitute a canal, into which the entire contents of the two cells thus connected enter, and combine together to form one mass which constitutes a single cell. This process is not always identical in different species. In Closterium (fig. 6) the middle of the cell-menibrane dehisces with a transverse fissure, and the entire contents from two contiguous opened cells coalesce into a single round or angular mass. Siebold says, with regard to the spores of green bodies which result from the union of the cells, that they are not in all cases developed into a single Closterium like spores; but that, as in the case of other Alge, such as Vaucheria and Edogonium, there are two sorts of spore

formations, and that under certain circumstances these green bodies represent a germ, capsule, or sporangium, in which, by a process of division, several young Closteria come to be perfected. The union of the cells of Didymoprium Borreri is seen in fig. 1.

The process above described appears to be one entirely confined to the vegetable kingdom, as it has never been observed amongst unicellular organisms, which are regarded as decidedly animal.

The process of swarming is one which, although a few years ago its distinguishing feature would have been regarded as entitling the organism exhibiting it to a place in the animal kingdom, is by Mr. Ralfs and other English naturalists regarded as purely vegetable. It has been observed in many species of Confervaceae, more especially in Achlya prolifera and Conferva area. The following is M. Agardh's account of this curious phenomenon in the latter plant. After describing the green matter in the joints, he says:-"The granules of which it is composed detach themselves from the mass one after another, and having thus become free they move about in the vacant space of the joint with an extreme rapidity. At the same time the exterior membrane of the joint is observed to swell in one point till it there forms a little mamilla, which is to become the point from which the moving granules finally issue. By the extension of the membrane for the formation of the mamilla, the tender fibres of which it is composed separating, cause an opening at the end of the mamilla, and it is by this passage that the granules escape. At first they issue in a body, but soon those which remain, swimming in a much larger space, have much more difficulty in escaping; and it is only after innumerable knockings (titubations) against the walls of their prison that they succeed in finding an exit. From the first instant of the motion, one observes that the granules or sporules are furnished with a little beak, a kind of anterior process always distinguishable from the body of the sporule by its paler colour. It is on the vibrations of this beak that the motion, as I conceive, depends; at least I have never been able to discover any cilia. However I will not venture to deny the existence of these; for with a very high power of a compound microscope one sees the granules surrounded with a hyaline border, as we find among the ciliated Infusoria on applying a glass of insufficient power. The sporules during their motion always present this beak in front of their body, as if it served to show them the way; but when they cease to move, by bending it back along the side of their body, they resume the spherical form; so that before and after the motion one sees no trace of this beak. The motion of the sporules before their exit from this point consists principally in quick dartings along the walls of the articulation, knocking themselves against them by innumerable shocks; and in some cases we are almost forced to believe that it is by this motion of the sporules that the mamilla is formed. Escaped from their prison, they continue their motion for one or two hours; and retiring always towards the darker edge of the vessel, sometimes they prong their wandering courses, sometimes they remain in the place, causing their beak to vibrate in rapid circles. Finally they collect in dense masses, containing innumerable gains, and attach themselves to some extraneous body at the batom or on the surface of the water, where they hasten to develop filaments like those of the mother plant." This cess, to which the name swarming has been given, has been observed by Mr. Ralfs, Dr. Hassall, and others in various pecies of Desmidiea, more especially in Sphæroplea crispa Draparnauldia tenuis. No similar movements to these have been anywhere observed amongst the ova of the animal kingdom.

The presence of starch in the Desmidiece is a third point relied on by Mr. Ralfs as distinguishing the vegetable kingdom. The existence of this substance is easily ascertained by the well-known reaction of iodine upon it. Meyen first covered this substance in the Algae, and Mr. Ralfs and others have confirmed the correctness of his observations. At the same time it should be stated that starch, although not found present in the tissues of the lower animals, has recently been detected in the brain of man by Mr. Busk (Microscopical Journal, vol. ii. p. 105). This may lead to the discovery of the existence of this substance more generally in the animal kingdom than has been hitherto supposed. The following reasons are given by Mr. Dalrymple, after ving an account of the structure of Closteria, for placing the species of this genus amongst animals:

1st. That while Closterium has a circulation of molecules greatly resembling that of plants, it has also a definite organ unknown in the vegetable world, in which the active molecules appear to enjoy an independent motion, and the parietes of which appear capable of contracting upon its contents.

2nd. That the green gelatinous body is contained in a membranous envelope, which, while it is elastic, contracts also upon the action of certain reagents, whose effects cannot be considered purely chemical.

3rd. The comparison of the supposed ova with cytoblasts and cells of plants precludes the possibility of our considering them as the latter, while the appearance of a vitelline nucleus, transparent but molecular fluid, a chorion, or shell, determines them as animal ova. It was shown to be impossible that these eggs had been deposited in the empty shell by other Infusoria, or that they were the produce of some Entozoon. 4th. That while it was impossible to determine whether the vague motions of Closterium were voluntary or not, yet the idea the author had formed of a suctorial apparatus forbade his classing them with plants.

On these reasons, Mr. Ralfs remarks, that the peculiar organ--the terminal globules-of the Closteria are as much vegetable as animal. That the throwing off the contents of the cell through chemical reagents, is as much vegetable as animal. "If fresh water touches Griffithsia setacea, the joints burst and spirt out their contents."" That the supposed ova contain starch, and are therefore vegetable. That he cannot discover that the orifices at the extremities of some of the Desmidiea are tubes, or that they possess a suctorial power.

1. Didymoprium Borreri, with the cells uniting to form the green matter. 2. Micrasterias crenata. 3. Euastrum oblongum. 4. Xanthidium armatum. 5. The same with a frond acquiring a new segment by division. 6. Closterium Lunula. 7. Pediastrum simplex. 8. Pediastrum Boryanum. 9. Ankistrodesmus falcatus.

The Desmidiea are all of an herbaceous green colour, and from this circumstance are easily discovered amongst the other microscopic beings with which they occur. They are mostly inhabitants of fresh water. Mr. Thwaites records two or three species from brackish water. They are remarkable for the very definite outline which their forms assume, especially in the genera Micrasterias (fig. 2), Euastrum (fig. 3), Xanthidium (fig. 4), and Pediastrum (figs. 7, 8). Their most obvious characteristic however is their evident division into two valves or segments. The point of union between the two segments is in general very definitely marked. In Pediastrum and Scenedesmus it is less obvio than other genera. It is at this point of union that the e

opens and discharges its contents. "An uninterrupted gradation," says Mr. Ralfs, "may be traced from species in which these characters are inconspicuous to those in which they are fully developed: thus in Closterium and some species of Penium there is no constriction; in Tetmemorus, in some Cosmaria, and in Hyalotheca, it is quite evident, although still but slight; in Didymoprium and Desmidium it is denoted by a notch at each angle; but in Sphærozosma, Micrasterias (fig. 2), and some other genera, the constriction is very deep, and the connecting portion forms a new cord between the segments, which appear like distinct cells, and are so considered by Ehrenberg and others." He further adds, "That the frond in Euastrum (fig. 3) and allied genera is really a constricted cell, and not a binate one, will, I am persuaded, be apparent to any one who traces the gradations mentioned above."

The manner in which the cells of the Desmidiea are mul

tiplied, is by means of repeated transverse divisions. This process may be seen in Euastrum, the new segments appearing at the constricted part of the original segments. At first the new segments appear as two roundish hyaline bodies formed of the substance of the connecting tube. These lobules increase in size, acquire colour, and gradually put on the appearance of the old portions. As they increase in size the original segments are pushed away from each other, and at length an entire separation takes place, each old segment taking with it a new segment to supply the place of the old one. This process is seen going on in fig. 5. This process is repeated again and again, so that the older segments are united successively, as it were, with many generations. This multiplication however has its limits, for the time comes when the segments gradually enlarge whilst they divide, and at length the plant ceases to grow. When this occurs no more segments are produced, the internal matter changes its appearance, increases in density, and contains starch-granules. The spore is now formed, which is to give birth to a new individual, and the old one perishes. The separate cells formed by this process of segmentation must be regarded as continuations of the same individual. They are like the grafts and buds from a tree; they continue the individual.

The reproduction of the Desmidica seems to take place in two ways: first, by the formation of granular contents in the cell, which have the power of moving, burst the cell, and produce the phenomena of swarming above referred to; and secondly, by the formation of a sporangium, or case containing spores, after the union or conjugation of the cells before described. The sporangia assume a variety of forms, and are sometimes covered with spines, and Mr. Ralfs says, "That the orbicular spinous bodies so frequent in flint are fossil sporangia of Desmidice, cannot, I think, be doubtful, when they are compared with figures of recent ones." Movements of the cell-contents of Desmidiea, similar to the cyclosis of higher plants, have been observed by Dalrymple, Bailey, and others. These movements consist of

definite currents of the cell-contents, passing in two opposite directions, the one along the side of the cell, and the other along the periphery of the gelatinous mass in their interior. Labarzewski, a German observer, states that these currents are intermittent, lasting each time for about seven seconds.

The part fulfilled by the Desmidiece in creation is little known. They undoubtedly purify the water in which they live in the same manner as other plants, and furnish food to a number of fresh-water animals. As they do not attach themselves to external objects they are seldom found living in running streams. They are sometimes found in the beds of large rivers, and several species are enumerated by Drs. Lankester and Redfern, in their report on the Microscopical Characters of the Water of the Thames.' The best places for procuring them are small shallow pools which do not dry up in the summer. Mr. Ralfs says, however, that the same species never occur in the same pools two years in succession. They prefer open moors and exposed places, and are rarely found in woods, shady places, or deep ditches. They are seldom found in turbid water of any kind. In this respect they are the opposite of their congeners the Diatomacea, which almost as a rule are found where the Desmidice are

not.

The best way of procuring them for examination is to take a piece of linen, lay it on the ground in the form of a bag, and then, by the aid of a tin box or ladle, scoop up the water, and strain it through the bag. After this process has en repeated a few times, the specimens of Desmidiea will

tinctly constricted at the junction of the segments, which are Frond simple from complete transverse division, disseldom longer than broad; sporangia spinous or tuberculated, rarely if ever smooth.

6. Micrasterias.-Lobes of the segments incised or bidentate. (Fig. 2.) Thirteen species.

7. Euastrum.-Segments sinuated, generally notched at the end, and with inflated protuberances. (Fig. 3.) Eighteen species.

8. Cosmarium.-Segments in front view neither notched nor sinuated; in end view elliptic, circular, or cruciform. Thirty-three species.

9. Xanthidium.-Segments compressed, entire, and spinous. (Figs. 4 and 5.) Six species. 10. Arthrodesmus.-Segments compressed, and having only two spines or mucros. Two species. 11. Staurastrum.-End view angular, radiate, or with elongated processes which are never geminate. Forty species.

12. Didymocladon.-Segments angular, each angle having two processes, one inferior and parallel with the similar one of the other segment, the other superior and divergent. One species.

***

Frond simple, from complete transverse division, generally much elongated, never spinous, frequently not constricted at the centre. Sporangia smooth.

13. Tetmemorus.-Frond straight, constricted at the centre, and notched at the ends. Three species.

14. Penium.-Frond straight, scarcely constricted at the centre. Eight species.

stricted at the centre, truncate at the ends. Seven species. 15. Docidium. Frond straight, much elongated, con16. Closterium.-Frond crescent-shaped or arcuate, not constricted at the centre. (Fig. 6.) Twenty-two species. 17. Spirotenia.-Frond straight, not constricted at the centre; endochrome spirally twisted. Two species.

****

Cells elongated, entire, fasciculated. 18. Ankistrodesmus.· Cells aggregated into faggot-like bundles. (Fig. 9.) One species.

*****

Frond composed of few cells, definite in number, and no forming a filament. (Sporangia unknown.)

19. Pediastrum.-Cells arranged in the form of a flattened star, their outer margin bidentate. (Figs. 7 & 8.) Elever species.

20. Scenedesmus.-Cells oblong or fusiform, entire, place side by side in a single row, but during division into tw rows. Six species.

(Ralfs and Jenner, British Desmidica; Siebold, O Unicellular Plants and Animals, in Mic. Journal, 1853 Meneghini, On the Animal Nature of Diatomacea, translate Plant, translated by Ray Society, 1854; Lindley, Vegetab by Ray Society, 1854; A. Braun, On Rejuvenescence in th Kingdom; Nägeli, Gattungen einzelliger Algen physiologis und systematisch bearbeitet, Zurich, 1849; Cohn, On th Natural History of Protococcus pluvialis, translated by Ra Society, 1854.)

DETINUE. In this action the defendant could, until recently, in all cases retain the chattels which the plaintiff sought to recover, on payment of the damages awarded by the jury as the alternative of not giving them up to the owner. If the plaintiff, therefore, was desirous of recovering the very chattel itself, he was obliged to seek relief in a court of equity, which, on the palpable ground of the remedy at law being insufficient, interfered, and compelled the defendant to make a specific delivery to the plaintiff of his property. It is no longer necessary to resort to the Court of Chancery for this purpose, the Superior Courts of Common Law having now the same powers as the Court of Equity to enforce the specific delivery of the chattels recovered in the action of detinue. (Common Law Procedure Act,' 1854.) DEXTRIN. [CHEMISTRY, S. 1; TISSUES, ORGANIC, S. 1.] DIALLAGE. [AUGITE.] DIANEA. [PULMOGRADA.] DIASPORE. [MINERALOGY, S. 1.] DIASTASE. [CHEMISTRY, S. 1.]

DIATOMACE, or DIATOMEÆ, a group of organised beings which naturalists have placed in the animal and vegetable kingdoms, according as they have regarded their structures as most allied to the one kingdom or the other. These organisms consist of a single cell, and are remarkable for possessing a hard shell-valve or frustule, which is composed of silex or flint, and which remains permanent after its organic tissues have perished.

The following is a definition of this group of beings by one of the most recent writers on this subject;-Plant a frustule; consisting of a unilocular or imperfectly septate cell, invested with a bivalve siliceous epidermis. Gemmiparous increase, by self-division; during which process the cell secretes a more or less siliceous connecting membrane. Reproduction, by conjugation, and the formation of sporangia. (W. Smith.) The Diatomacea are endowed with the power of motion; and when this function was supposed to be peculiar to the animal kingdom, it is not to be wondered at that the first ebservers of these organisms referred them to the animal kingdom. Ehrenberg, in his great work on the Infusorial Animalcules,' greatly enlarged our knowledge of this family, and added to the forms that were already known. He regarded them, as well as the Desmidiece, and other beings which are now generally referred to the vegetable kingdom, as animals. The following are the principal points on which he relied for assigning to them this position:

6

1st. The Diatomaceae exhibit a peculiar spontaneous movement, which is produced by certain locomotive organs. 2nd. A large number of them have in the middle of the lateral surface an opening about which round corpuscles are staated, which become coloured blue when placed in water containing indigo, just as many of the Polygastric Infusoria. 3rd. The shells of the Diatomacea resemble in structure and conformation those which are seen in the Mollusca and ther animals.

These arguments are met on the other side by the stateneat, that spontaneous movement is now known not to be ally animal, as the spores of many Algae, and their etire fronds are known to be actively motile. In the next pace the colouring of the interior by indigo also takes pace in truly vegetable structures.

The complex structure of the minute siliceous frustules of Diatomacea is a fact that has struck many observers. It ainly is without a parallel in the vegetable kingdom. leiden in his 'Principles of Scientific Botany,' after giving minute analysis of the siliceous structure of Navicula dis (fig. 6 represents this genus), says, "Such an artificial complicated structure amongst plants has no explanation entirely without significance. In all true plants we the silica present in a very different form, as minute ales or drops, and distributed through the substance of the wall." Again, in another place he says, "This curious tare is wholly without analogy in the vegetable kingdom, cannot be derived from the laws of vegetation with Fich we are at present acquainted."

More recently Professor Meneghini has come forward as an vocate of the animal nature of Diatomaceœ. In a very laed and remarkable essay, published at Venice in 1845, he

"If we suppose them to be plants, we must admit every bale, every navicula, to be a cell. We must suppose this with walls penetrated by silica, developed within another cil of a different nature, at least in every case where there is a distinct peduncle or investing tube. In this siliceous

wall we must recognise a complication certainly unequalled in the vegetable kingdom. It would still remain to be proved that the eminently nitrogenous internal substance corresponded with the gonimic substance, and that the oilglobules could take the place of starch. The multiplication would be a simple cellular deduplication (sdoppiamento), but it would remain to be proved that it takes place, as in other vegetable cells, either by the formation of two distinct primitive utricles or by the introflection or constriction of the wall itself. Finally, there would still remain unexplained the external motions and the internal changes, and we must prove Ehrenberg's observations on the exterior organs of motion to be false. But, again, admitting their animal nature, much would remain to be investigated, both in their organic structure and their vital functions; excepting this, so far as we know, we have only one difficulty to overcome, that of the probably ternary non-azotised composition of the external gelatinous substance of the peduncles and investing-tubes. But as the presence of nitrogen is not a positive character of animal nature, so the absence of it is not a proof of vegetable. And in order that the objection should really have some weight, it would be well to demonstrate that this substance is isomeric with starch. For then, supposing all the arguments in favour of the animal nature of Diatomea were proved by new and more circumstantial observations, this peculiarity, if it deserve the name of objection, might still be regarded as an important discovery. We should then have in the animal as well as in the vegetable kingdom a ternary substance similar to that forming the basis of the vegetable tissue."

Of the chemical composition of the Diatomaceæ little satisfactory has at present been made ont. Professor Frankland of Manchester, according to the Rev. W. Smith, whose work on the British Diatomacea is one of the last that has hitherto been published, has found that a large amount of iron exists in the state of a silicate or protoxide in the siliceous frustules, which probably accounts for the brown or yellow colour of these organisms. On the application of tincture of iodine the internal membrane contracts on its contents, and converts these from a golden-yellow to a bright green. On the addition of sulphuric acid they exhibit a deep brown hue.

The fact which is most relied on to support the vegetable nature of the Diatomacea, by those who advocate this view, does not appear to have been known to Meneghini, and that is the conjugation of the cells of which they are composed in the same manner as in the Desmidiea. [DESMIDIE, S. 2.] This discovery was made by Mr. Thwaites, and observed in species of Eunotia (fig. 1), in Epithemia gibba and E. turgida (fig. 19), Fragilaria pectinalis, and other species. This process takes place as follows:-Two individuals closely approximated dehisce in the middle of their long diameter, whereupon four protuberances arise, which meet four similar ones in the opposite frustule. These indicate the future channels by which the endochrome of the two frustules becomes united, as well as the spot where subsequently the double sporangium is developed (figs. 8, 19). From the sporangium the new individuals are developed. This process is precisely analogous to what takes place in the Desmidieo, so that the frustules of the Diatoms must be regarded as cells of the same individual. "If we duly consider this fact," says Mr. Thwaites, "how much does it exalt the lower tribes of plants in our estimation! since we may contemplate an individual plant of them not as the single phyton-not as the single frond-not as the single cell-but it may be as the aggregate of thousands of these; -view it occupying as much space and exercising as great au influence in the economy of nature as the largest forest-tree !"

The mode by which the cells are multiplied amongst the Diatomacea appears to be strictly in accordance with what occurs generally in the vegetable kingdom. This process is one of self-division. The first step is the fission or division of the internal cell, "probably by the doubling-in of its membranous wall, and consequently the separation of the endochrome, or cell-contents; the central vesicle or cytoblast also dividing into two parts, which remove to a little distance from each other; these movements being simultaneous with a retrocession of the epidermal valves and the formation of the siliceous connecting-membrane already described. In the centre of the enlarged frustule, in exact apposition to the original valves and closely applied to them, there are now found two new valves, covering the surface of the cell-membranes along the line of fission. The divided portions of the endochrome