THE COMMON FROG* VIII. THE HE skeleton of the ankle as developed in the frog's class presents us with some characters, which, more than even those of the wrist, suggest the passage of the line of affinity directly from Batrachians to mammals, leaving both reptiles and birds on one side. There are other matters, however, more important than this. It has been remarked that the wrist shows an FIG. 52. FIG. 51. FIG. 51. Right foot of Emeu. a, astragalus; d-d4, second, third, and fourth digits; m, metatarsals anchylosed together except at their distal ends; t, tibia; fa, distal tarsal element. FIG. 52.-Left foot of a Monitor Lizard (Varanus). f, fibula; mi-m5, the five metatarsals, m being that of the hallux; , tibia; 1, astragalocalcaneum ; 2, cuboides; 3, ecto-cuneiforme. In the first place we meet in the frog with certain extra ossicles in the inner side of the foot, which present the appearance of a broad rudiment of an extra digit on the inner side of the great toe. Now we find a structure very B FIG. 56.-Elongated tarsus of Lemuroids. Left-hand figure, tarsus ot Cheirogaleus; right hand figure, tarsus of Tarsius. A. calcaneum; B. cuboides; C, naviculare. is wanting in most reptiles and in all birds. The same FIG. 53' FIG. 54. por FIG. 53. Skeleton of posterior extremity of an eft. FIG. 53. Bones of foot of Frog.-a, astragalus; c, os calcis; ac, united tions of these bones; li, extra ossicle of inner side of foot; cb, ossicle representing cuboid and other tarsal bones-1, 2, 3, 4, 5-the five metatarsals. similar in form in animals remote enough from Batrachians, yet rarely do we find such in any intermediate kinds. Thus in certain tree-porcupines the ankle is furnished in like manner-another instance of the independent origin of strikingly similar structures. * Continued from p. 150. FIG. 57.-Tadpole of Bull Frog, partly dissected, to show the muscles of the tail and the branches of the 8th nerve or the vagus. a, great lateral branch giving off-b, a dorsal branch, and c, the lateral branch (or nervus lateralis); d, branches descending and passing along the branchial arches. The descending branches seen behind the branchial nerves on the side of the belly are not branches of the vagus at all, but spinal nerves, which come out from beneath the muscles and pass down under the nervus lateralis, and without having any communication with it. observation may be repeated with far greater force as regards the ankle. FIG. 59. FIG. 58. FIG. 58.-Anterior muscles of the Trunk: the pectoralis major of the right side and the left external oblique being removed. 1, pectoralis major; 2, pectoralis minor; 3, subclavius: 4, serratus magnus; 5, internal intercostals; 6, external oblique; 7, internal oblique: 8, linea alba. FIG. 59.-Deeper Abdominal Muscles-the external oblique being removed from the left side of the body, and the internal oblique and part of the rectus also, from its right side. 1. the internal oblique; its outer tendon (2) is cut and reflected from the outside of the rectus to show its deeper tendon (3), which passes within the rectus except towards the pubis; 4, transversalis; 5, its fascin; 6, sheath of the rectus-pear the pubis, the conjoined aponeuroses of the abdominal muscles pass in front of that muscle; 7, pyramidalis; 8, rectus of left side, showing the tendinous intervals, or lineæ transversa. In all birds, on the contrary, not only is there no motion between the ankle-bones (as a whole) and the shin-bone, but the two rows of ankle-bones actually anchylose respectively with adjacent parts--the row nearer the leg coming to form one with the shin-bone; the second row coming to form one with the bones of the foot. Thus in birds the motion of the foot on the leg takes place not FIG. 61.-Superficial Muscles of Extensor Side of Leg and of parts of Trunk and Tail of Menopoma. ES, erector spine-directly continued into dorsal half of tail; ELD, extensor longus digitorum pedis; FC, femoro-caudal; GMx, probably rectus femoris; I, muscle resembling iiacus; ILC, ilio-caudal; IP, ilio-peroneal; RF, part of great extensor of thigh; SM and ST, muscles like the semi-membranosus and semi-tendinosus. bited to us by certain beasts than it does with that which is possessed by any bird or of most reptiles. The frogs and toads, however, differ from the Urodela and present us with a peculiar condition of the anklebones, in that the two which represent the bones of the first row are so greatly elongated as to give to the limb an additional segment-as it were two "long bones" more. We should search in vain through every other order of the Batrachian class, through every known group of birds and reptiles, both living or fossil, to find any analogous structure. None of the lowest mammals, no marsupial, no rodent, no insectivorous or carnivorous beast, no hoofed mammal, presents us with anything of the kind. Nevertheless, at almost the other end of the series, in the very FIG. 60.-Superficial Muscles of the Perch. The fin-rays of all the fins are cut off. 1, great lateral muscle, showing the numerous vertical tendinous intersections slightly but variously inflected; 2, small superficial muscles inserted into the fin-rays of the dorsal and ventral fins; slender longitudinal muscle running (in the interval of the summits of the two great lateral muscles) between the dorsal and caudal fins; 5, similar muscle on the ventral margin, which also appears between the anal and ventral fins; 6, small radiating muscles of the caudal fin; 7. part of the great lateral muscle inserted into the skull; 8 and 9, elevators of the operculum; 10, elevator of the palato-quadrate arch; 11 and 12, muscu lar mass by which its contraction closes the jaws; 13, superficial muscles of the pectoral fin; 14 and 15, muscles of the ventral fin. between the ankle and the shin-bone but between the two rows of ankle-bones. The same thing to a less degree takes place in reptiles; the ankle-bones do not indeed anchylose with the shinbone and foot respectively, but they nevertheless unite with those parts so firmly that motion takes place between highest order, that to which man himself belongs, we actually find a very similar development. 66 Amongst the very peculiar beasts which inhabit the island of Madagascar, there are certain small creatures, Half-Apes," belonging to the genus Cheirogaleus, in which two of the ankle-bones are elongated in a manner similar to that of the frog. The same character is more marked in an African genus of half-apes (Galago), and still more so in a third half-ape (Tarsius), from the island of Banca. Now it is absolutely impossible to believe that a special genetic affinity connects together by a peculiarly common descent, Half-Apes and Frogs! We are then driven to the conclusion that we have here again a striking similarity of structure in two instances which are quite independent in their origin. That the power of rapid and prolonged "jumping" does not carry with it as a necessary consequence the elongation of ankle-bones, is demonstrated by the fact that in other animals which, to say the very least, jump no less than do these half-apes--as for example in the kangaroos, jumping shrews, and jerboas—it is not bones of the ankle but bones of the foot proper, which take on an augmentation in length. The Muscles of the Frog We may now pass to the consideration of some points exhibited by another set of structures—namely, the muscles. The muscles of an animal constitute its flesh, which as the most ordinary inspection shows us, is composed of different portions of soft fibrous substance separated from one another by interposed layers of membrane. Each such portion, so separated, is a muscle, and is attached at its two ends to two parts (bones or what not), which may be adjacent or more or less distant. The fibres which compose it have the remarkable property of contracting under certain conditions, and, when contracted, the whole muscle is shorter and thicker than before, and the two parts to which it is attached become consequently approximated. Muscles may be large expanded sheets of flesh (as in the abdomen) or long and more or less narrow, as in the limbs. Muscles are said to be "inserted," or to "take origin from" the parts to which they are attached, and they may be so inserted either by their own muscular fibres or by the intervention of a tough membrane or a dense fibrous cord called a "tendon." All the motions of an animal are produced by means of the contractions of its muscles pulling the bones, which act as so many levers (of different kinds according to circumstances), and so effecting locomotion, These muscular contractions are in life produced by the agency of certain of the nerves proceeding from the nervous centres, i.e. from the brain and spinal marrow, and which carry an influence outwards to the muscles. Other of the nerves so proceeding convey an influence inwards to the nervous centres from an irritated portion of the body's surface. The muscles, however, especially in the frog may, for a time, be made to contract after death by direct irritation of the nerves themselves. After the skeleton, it is the muscular formation of the body which mainly determines its general form and aspect, though occasionally-and often in the Frog's order-the voluntary inflation of the lungs will alone produce a vast modification in an animal's appearance. The curious and grotesque resemblance which exists between the figure of the adult frog and that of man has been a common subject of remark. It may then be less surprising to some to learn that there is a great degree of resemblance between the muscles of the Rational and of the Batrachian animals; though the much greater gulf which separates the Batrachian than the Reptilian class from mammals may lead others to anticipate a greater divergence than in fact exists. The frog, however, in its immature stage of existence, is widely different from the adult in its muscular (or myological) furniture, and this from one obvious reason. 66 "Muscles" are, as we have shown, par excellence, organs of motion," and the motions of the tadpole are essentially different from those of the frog. The frog, as all know, progresses on land by jumps, and swims through the water by a series of movements which are in fact aquatic jumps. This action is familar to many of us, not only from observation but also by imitation (the frog being a swimming-master given us by nature), but it is none the less a mode of swimming which is very exceptional indeed. The tadpole progresses through the water in a very different manner, namely, by lateral undulations of its tail, which is the usual mode of swimming among vertebrate animals-that made use of by sharks and porpoises, as well as by the overwhelming majority of fishes. Studying the life-history of this one animal, then, we become acquainted with a process of direct transition from the condition of a fish to that of a quadruped, as regards a most important group of organs. In ourselves, the back is provided with muscles which extend along its length in a complex series of longitudinal divisions, from the middle line outwards. The abdomen of man is inclosed and protected by successive muscular layers laid one upon another, the fibres of the successive muscles being differently directed. Thus we have (1) the external oblique (the fibres of which pass obliquely downwards and backwards, (2) the internal oblique (the fibres of which pass obliquely downwards and forwards), (3) the Transversalis (with transverse fibres), and (4) the Rectus abdominus (situated in the middle line of the body, and with fibres directed anteroposteriorly). In the frog we also meet with the vast sheets of muscle with oppositely directed fibres (the external and internal oblique) and with a median, antero-posteriorily directed rectus muscle. A very different condition exists in fishes, where there is indeed a median antero posteriorly directed rectus, but where the abdomen and tail are encased with a mass of muscular fibres not arranged in superimposed sheets, but as a series of narrow segments separated from each other by layers of membrane. The edges of these membranous layers, when the skin is removed, appear as a successive series of undulating lines proceeding from the back to the belly. Now the tadpole exhibits a muscular condition (Fig. 56) quite similar to that of the fish, and in the great persistent larva the axolotl, we find no truly oblique abdominal muscles, but only as it were a hypertrophied rectus. In other species of the frog's class which retains a tail throughout life, the marked superimposed lamellæ are distinctly developed, but more or less distinct traces are also retained of the successive membranous partitions separating the muscular segments of both the dorsal and ventral regions. Another stage of development may be detected in the tail-muscles of certain reptiles. Here the membranous partitions have become drawn at short intervals from above downwards out into a formal shaped condition, so that the muscular fibres enclosed, assume the forms of cones. Moreover, the apices of the membranes enclosing the cones, become denser in substance, and so modified into ligaments. We come thus to have a key to the process of development, by which the muscles of the back may be conceived to have arisen. The muscles of the back may be conceived as having arisen through increasing obliquity, conical prolongation, and partial detachment (from muscle) of the separating membranous lamella; the produced ends becoming condensed with firm tendons directed more or less obliquely forwards. The muscles of the abdomen may be conceived as having arisen through atrophy, in that region, of the separating membranes and subsequent splitting up of the muscular mass into super-imposed sheets of differently directed fibres. This filiation between piscine and mammalian myology could hardly have been detected but for the remarkable series of gradations which the frog's class exhibits gradations both between species, and between different ON (To be continued.) BEES VISITING FLOWERS N the cliffs at Llwyngwril, near Barmouth, Lathyrus sylvestris grows in large patches, and is freely visited by humble-bees. Where a plant grows in considerable masses, a great number of bees are naturally attracted, and the competition among them becomes severe. In this case the flowers are not sucked in the usual manner, but the bees bite holes through the corolla, and obtain in this way illegitimate access to the honey. Hermann Müller has shown that when flowers grow in any quantity, they are so diligently worked at by the bees that only comparatively a few contain any nectar; it is therefore important for the bees to find out as quickly as possible whether a flower is worth anything or not. These holes, bitten through the corolla, enable the bees to visit the flowers more quickly, and are thus a great saving of time. He also says that, although the bee which first gnaws the hole loses time in doing so, yet the advantage of being able to get the honey from the young and as yet unvisited flowers, fully makes up for the loss of time. In L. sylvestris, as in many Leguminosa, the honey is secreted within a nectary formed by the filaments of nine of the stamens soldered together. The trough-like cavity thus formed is covered in above and converted into a tube, by the tenth stamen. But at the base, where the trough enlarges into a bulb, the stamen is not wide enough to cover it, so that it leaves a pair of holes piercing the tube one on each side. It is through these "nectarholes," as they are called, that the bee, after passing its proboscis down the tube of the corolla, or, as in the case already mentioned, through the holes bitten at its base, gains entrance to the staminal tube, in its search for nectar. In L. sylvestris the hole is gnawed through the tube of the vexillum, close to the edge of the calyx, and exactly over the left nectar-hole. (Throughout this paper I mean the right and left of an observer looking at the front of the flower.) I think the reason of this constant choice of the left side of the corolla is that the left nectar-hole is usually somewhat larger than the right. I found this to be the case in sixteen out of twenty-four specimens of the wild L. sylvestris, and in eleven out of sixteen in the garden variety (the Everlasting Pea). It is difficult to say how the bees have acquired this habit. Whether they have discovered the inequality in the size of the nectar-holes in sucking the flowers in the proper way, and have then utilised this knowledge in determining where to gnaw the hole; or whether they have found out the best situation by biting through the vexillum at various points, and have afterwards remembered its situation in visiting other flowers. But in either case they show a remarkable power of making use of what they have learnt by expe emerges indifferently to the right or left of the tenth stamen. I am inclined to believe that the want of symmetry in the growth of the pod and the inequality in the size of the nectar-holes are in some way correlated, and that both are connected with a third asymmetrical character in the flower of this species. In most Lathyri the brush of hairs on the pistil is directed straight backwards towards the stalk of the flower. This is the case with L. pratensis, and also with the flower-buds of L. sylvestris, while very young; but, as they get older, the pistil rotates on its own axis, so that, in the adult flower, the brush is turned towards the left. I have often watched the bees sucking the flowers of the Everlasting Pea in the ordinary way, and have observed that the pistil, in consequence of being slightly bent as well as twisted on its own axis, emerges from the keel on the right side of the bee. The function of the brush is, as Mr. Farrer has shown (NATURE, vol. vi. p. 479, 1872), to sweep the pollen out of the keel, so that it may be transferred to the bees visiting the flower, and may be in this way subservient to the cross-fertilisation of the species. I believe that the twisting of the pistil helps to ensure this end, since in consequence of the brush being turned towards the left it rubs against the bee and smears it with pollen. Thus the mechanism for ensuring the cross-fertilisation of the plant is made more complete. At present the supposition that the asymmetrical character of the pistil is connected with the above described peculiarities and in the growth of the pod, is merely a conjecture. These facts have a certain bearing on a peculiarity in the structure of the staminal tube in Phaseolus multiflorus, the Scarlet-runner. This flower, in common with many Leguminosa, has a pair of nectar-holes at the base of its staminal tube; but the tenth_stamen differs, as far as I know, from that of any other Leguminous plant, in possessing a little flap which projects from its upper surface just in front of the nectar-holes, and which almost completely blocks up the tube of the corolla. Mr. Farrer supposes (loc. cit. p. 480) that by pressing with its proboscis against this flap the bee levers up the tenth stamen, and in this way passes its trunk into the staminal tube. If this occurs at all, it must be like gnawing holes in the corolla, an illegitimate way of treating the flower, since it is impossible to believe that it should have well developed, but totally useless, nectarholes. I believe the true function of this curious little flap to be as follows:-In many Papilionaceæ, Lathyrus for instance, the insect visiting the flower rests on a platform which is formed of the carina and the expanded aiæ, but in the Scarlet-runner this platform is made up by the alæ alone, the carina being tightly coiled into a spinal close up to the entrance to the tube to the corolla. The ale are attached, one on each side to the proximal part of the carina, so that when an insect rests on them, its weight bears on the carina, and causes the pistil which is contained in it as in a sheath to be forced out. The direction of movement of the pistil is downward and to the left, so that a bee resting on the expanded alæ and pushing in its head to the left of the coiled-up carina would come in contact with the pistil as it darted out of its The united filaments not only form the nectary, but sheath; but if the insect went to the right of the coil it also a sort of casing in which the ovary is enclosed; and would escape the pistil altogether. The end of the pistil out of which the growing pod has to break its way as it is covered with hairs, and performs the same function as increases in size. In Vicia cracca it does so by lifting up the brush in Lathyrus in smearing the bee with pollen. the tenth stamen, but in most Lathyri the filament is too It is, therefore, of great importance for the cross-fertilisastiff to allow of such a movement, and the growing pod tion of the plant that the bees should go to the left of the was to squeeze its way between it and the edge of the coil. As a matter of fact they all but invariably do go to trough formed by the nine united filaments. In doing the left; the very few bees that I have seen going to the this it enlarges and at last splits open one of the nectar-right appear dissatisfied and unable to find their way into holes. In L. sylvestris the left nectar-hole, usually the larger of the two as I have before said, is almost always the one which is thus opened. In L. pratensis, on the other hand, where the nectar-holes are equal, the pod rience. the corolla. Now to reach the nectar-holes the insect's proboscis has to pass down a tunnel formed above by the tube of the vexillum, below by the upper surface of the tenth stamen; the entrance into this tunnel is a narrow archway leaning towards the left, i.e. having its highest point to the left of the middle point of its base. As before stated, the flap almost blocks up the tunnel, so that to get to the nectar-holes the proboscis must pass over the top of the flap, and must therefore travel along the highest part of the tunnel, but since at the entrance arch the highest point is to the left, the bee finds it necessary to go to the left of the coiled-up carina to reach the nectarholes in the easiest way. If this view of the function of the flap, when considered in relation with the disposition of the pistil, carina, &c., be correct, it adds another instance to the long list of mechanisms for ensuring the cross-fertilisation of flowers by means of the visits of FRANCIS DARWIN insects. stances, was again mooted by Alquier at the Council of the Ancients, on the 27th Nivose, year 7, which urged the great advantage of such an institution to workmen, by saying that it is of more use showing them articles than merely speaking of them. It was not, however, until the 12th Germinal, year 7, that the buildings of the priory of St. Nicholas of the Fields were put into the possession of the members of the Conservatoire, who were then composed of Le Roy, Conti, Molard, and Benvelot, designer. The names of these savants, and that of Montgolfier, who soon after replaced Le Roy, did not allow of any comparison being made between the functions of these lecturers and those who are differently named now-a-days. "At length, in the year 8, all the models and machines belonging to the State were definitively removed to this THE FRENCH MUSEUM OF PHYSICAL AND building, and formed collections destined solely for the MECHANICAL SCIENCE THE following of Conservatoire des Arts-et-Métiers, HE following official report of General Morin, the Paris, to the Minister of Agriculture and Commerce, which we take from the Journal of the Society of Arts, furnishes some interesting details as to the present condition of this magnificent educational establishment, the like of which, dealing as it does with experimental and mechanical science, is entirely wanting in our country, although in the British Museum, the student of Natural History finds all he needs. "The total number of persons who attended the lectures of the fourteen professors amounted in 1872 to 135,443, at 559 lectures, or in the proportion of 241 to each lecture. The smallest number of lessons given by any one professor was 40, from the opening in the commencement of November, until the last days of April. The total number of persons attending is smaller than in preceding years, which is explained by the decrease of the floating population of Paris. This year, as in all others, the decrease commenced when the days got longer, and work kept the people in the workshop. "I would here limit this report if I did not think it necessary to add a few words upon the means of instruction which the Conservatoire offers to the public and the working-classes of all ranks. "This establishment, as is known, owes its origin to the illustrious Vaucanson, inspector of factories, who, after having made at the Hotel du Montagne, Rue de Charonne, a collection of machines, instruments and tools, for the instruction of workmen, presented it to the Government, on the sole condition that its original purpose should be maintained. Louis XVI. accepted the gift by an act of council, and the illustrious Vandermonde, member of the Academy of Sciences, was named administrator and conservator of this first industrial museum. Later, by the decrees of the 15th and 18th of August, 1793, the Convention created a temporary commission of arts, to put a stop to the dispersion of objects of art, science, and industry. This commission succeeded in collecting a large number in a depot formed at the Hotel d'Aiquillon, Rue de l'Université. The value of these collections soon after determined the Convention, upon the report of Gregory, to make a decree, the 19 Vendémaire, year 3, that there should be formed in Paris, under the name of Conservatoire des Arts-et-Métiers, a public collection of machines, models, tools, drawings, descriptions, and books of all kinds of arts and science, the use of which should be explained by three lecturers attached to the establishment. "It may be well to mention that the title of 'demonstrateur' or lecturer, often corresponded to that of professor, and that the professors of the Jardin des Plantes remained long after they had commenced giving regular courses. However that may be, the organisation of the Conservatoire, which was checked by several circum instruction at sight. The functions implied by the title of lecturer were never exercised, and this will easily be believed when it is said that the numerous visitors who are attracted by the rich collections sometimes amount to 200,000, which makes all verbal explanation on the spot impossible. But that which is not possible to do for the public has been for a long time afforded by the Conservatoire to persons who are really desirous of information. A complete and methodical catalogue has been made out and published, and to it are added, from time to time, all new acquisitions; this has already passed through four editions. The galleries have been systematically classified, a guide has been placed in each, who, if he cannot give any practical explanation, can at least show where such and such a model is to be found, each of which is ticketed and numbered, both in the catalogue and in the inventory. Should an engineer or a workman wish to examine separately a machine or machinery, a study card for the necessary time is given to him. Or should any more complete information or explanation be required, either the curator of the collections, the under-director, or the director, is always ready to furnish them, their office being freely open to all. "The staff in charge of the collections consists of the conservator, an assistant conservator, and of fourteen chosen guardians, who, for the most part, are picked from old non-commissioned officers or soldiers. The wish to give explanations by these, even with the aid of written details for the 9,000 models or articles which are there, would lead to great errors and confusion by a zealous but a badly instructed staff. In asking that popular conferences, such as are held at the Polytechnic Institution of London, should be introduced here, account has not been taken of the great difficulties which stand in the way, and greatly exaggerated ideas exist as to their value. "It is not by common and vulgar explanations that the principles of Science can be spread amongst our workmen, and the facts and experience which are so necessary; their minds and intelligence are developed enough, so no fear need be had to speak to them on difficult scientific questions, if it is done with wisdom. "All the professors who have followed this mode of teaching have often been convinced, on meeting some of their old hearers in workshops, that what may be termed the knowledge of truth and scientific principle has more deeply entered into their minds than into that of scholars of more celebrated schools. Hence it was not without reason that, in 1819, a decree of the king, brou ht about by the respected Dean, M. le Baron Charles Dupin, added to the instructions at sight given by the collections, that of oral instruction in the amphitheatres, by professors chosen from among the ranks of science. The number of chairs, at first only three, is now fourteen, and the half of the professors are members of the Institute, who diffuse and popularise science, the progress of which they promote by their labours. This instruction, unique of its kind in Europe, only takes place during winter; it is free |