superficial layer, and in turn invested by a thin cuticle. The superficial layer is connected with the central protoplasmic parenchyma by numerous radiating, branched, and anastomosing filaments of sarcode. The luminosity appears to reside in nucleated cellular bodies in the outer layer of the central protoplasm-that is to say, in the peripheral layer of sarcode immediately below the cuticle. DISTRIBUTION OF THE INFUSORIA IN SPACE AND IN TIME.— The Infusoria have at the present day an almost universal distribution, being found in all collections of fresh and salt water, where decaying organic matter is present, and where the other conditions of life are favourable. A few are parasites in the interior of other animals (Opalina), but the true affinities of these is doubtful. Owing to the fact of their generally wanting any hard structures which could have been preserved in a fossil condition, no true Infusoria* can be said with certainty to have existed in former periods of the earth's history, though they have doubtless abounded in past time as now. The only possible exceptions to this statement are certain microscopic bodies which occur in the Chalk-flints, and which Ehrenberg considered to be the protective carapaces of Peridinium and allied forms of Flagellate Infusoria. LITERATURE. [In the subjoined list, as well as in those which will be subsequently given, it is hardly necessary to say that nothing further will be attempted than to furnish the student with a brief and limited selection from the numerous works and memoirs relating to the animals belonging to each subkingdom. It has also not appeared needful to cite the names of wellknown manuals and text-books of zoological science, save where these contain special information.] GENERAL WORKS. 1. "Die Klassen und Ordnungen des Thier-Reichs,” vol. i. Amorphozoa. Bronn. 2. "Manual of the Protozoa." Greene. 3. "Micrographic Dictionary. Griffiths and Henfrey. 4. "The Microscope and its Revelations." 5- "Life Histories of Animals." Packard. GREGARINIDA. Carpenter. 6. "Icones Histiologicæ," vol. i. p. 7. Kölliker. * "Fossil Infusoria " are often spoken of as forming more or less extensive deposits in the earth's crust, but the organisms so named are really Diatoms and Polycystina. 7. "Ueber die Natur der Gregarinen." 'Müller's Archives für Anatomie,' 1848. Stein. 8. "On a new Species of Gregarina to be called Gregarina gigantea” 'Quart. Journ. Microscop. Science,' vol. x., 1870. Van Beneden. 9. IO. II. 12. 13. 14. 15. MONERA. Monographie der Moneren." Jenaische Zeitschrift für Medecin und Beiträge zur Kenntniss der Moneren." Schultze's 'Archiv für Mik- АМЕВЕА. 'Études sur les Infusoires et les Rhizopodes,” vol. i. p. 413. Claparède and Lachmann. "Ueber die Einzelligkeit der Amoeben." Zeitschrift für Wiss. Zoologie,' 1855. Auerbach. "On some Fresh-water Rhizopods." 'Quart. Journ. Microscop. Science,' 1869-71. Archer. "Fresh-water Rhizopods." Annals of Nat. Hist.,' ser. 3, vol. xiii., 1864. Carter. "Amoeba villosa," &c. Annals of Nat. Hist.,' ser. 3, vol. xi., 1863. Wallich. FORAMINIFERA. 16. "Introduction to the Study of the Foraminifera" (Ray Society'), 1862. Carpenter. 17. "Ueber den Organismus der Polythalamien," 1854. 18. "On the Recent Foraminifera of Great Britain 1858. Williamson. Schultze. ('Ray Society'), 19. "Researches on the Foraminifera." Phil. Trans.,' 1856-57. Carpenter. 20. "Handbuch der Paleontologie," vol. i. pp. 61-114, 1876. Zittel. 21. "Carboniferous and Permian Foraminifera" (with a general Introduction). Monographs of the Palæontographical Society,' 1876. H. B. Brady. 22. "Mikrogeologie." Ehrenberg. 23. "Foraminifères Fossiles du Bassin Tertiaire de Vienne." D'Orbigny. RADIOLARIA. 24. "Ueber die Thalassicollen, Polycystinen, und Acanthometren des Mittelmeeres." Abhandl. d. K. Akad. Berlin,' 1858 (also in 'Quart. Journ. Microscop. Science,' 1859). J. Müller. 27. "Fortsetzung der Mikrogeologischen Studien," &c. Abhandl. d. K. Akad. Berlin,' 1875. Ehrenberg. 28. " 'On Thalassicolla." Annals of Nat. Hist.,' 1851. Huxley. 29. "Actinophrys sol." "Quart. Journ. Microscop. Science,' 1853. Kölliker. 30. "Heliozoa." Quart. Journ. Microscop. Science.' Archer. “Anatomy_and_Physiology of the Spongiada." Phil. Trans.,' 1859. Bowerbank. 32. "British Spongiada" (Ray Society'). Bowerbank. Oscar Schmidt. 33. "History of British Sponges and Lithophytes." Johnston. 1842. 34. "Die Spongien des Adriatischen Meeres," 1862-66. 35. "Die Kalk-Schwämme." Hæckel. 1872. 36. "Anatomy and Classification of Sponges.' 1875. Carter. 'Annals of Nat. Hist.,' 37. "Vitreous Sponges." 'Annals Nat. Hist.,' 1868. Wyville Thom son. 38. “Classification of Sponges." Proc. Zool. Soc.,' 1867. Gray. 39. Development of the Marine Sponges.' Annals Nat. Hist.,' 1874. Carter. 40. "Development of the Calcispongiæ." 'Annals Nat. Hist.,' 1875. (Translation.) Metschnikoff. 41. "The Spongia ciliata as Infusoria flagellata.” Hist.,' 1868. James-Clark. 42. "The Depths of the Sea," 1873. Wyville Thomson. 'Annals Nat. 43. "On Holtenia." Phil. Trans.,' 1870. Wyville Thomson. 45. “Introduction à l'étude des Éponges fossiles," 1859. De Fromentel. 46. "Ventriculitide of the Chalk." 'Annals Nat. Hist.,' 1847-48. Toulmin Smith. INFUSORIA. 47. "Die Infusionsthierchen als Volkommene Organismen," 1838. Ehrenberg. 48. "Infusoires," 1841. Dujardin. 49. "Der Organismus der Infusionsthiere," 1867. Stein. 50. "Etudes sur les Infusoires et les Rhizopodes." 'Mem. de l'Institut National Genevois,' 1858-61. Lachman and Claparède. 51. "Recherches sur les organes générateurs et la reproduction des Infusoires." 'Comptes Rendus,' 1858. Balbiani. 32. “Untersuchungen ueber den Bau und die Naturgeschichte der Vorticellen. Archiv für Naturg.,' 1870. Greeff. 53. "Zur Morphologie der Infusorien." 'Jenaische Zeitschrift,' vol. vii., 1873. Hæckel. 54 "Ueber einige neue pelagische Infusorien." "Jenaische Zeitschrift,' vol. vii., 1873. Hæckel. 55. "History of Infusoria." Pritchard. 36. "Recent Progress in our Knowledge of the Ciliate Infusoria." Proc. Linn. Soc., 1875. Allman. 57. "Flagellate Infusoria." 'Annals Nat. Hist.,' 1868. James-Clark. G 3. GENERAL CHARACTERS OF THE HYDROZOA. 4. Ex THE Sub-kingdom Cælenterata (Frey and Leuckhart) may be considered as a modern representative of the Radiata of Cuvier. From the Radiata, however, the Echinodermata and Scolecida have been removed to form the Annuloida, the entire sub-kingdom of the Protozoa has been taken away, and the Polyzoa have been relegated to their proper place amongst the Mollusca. Deducting these groups from the old Radiata, the residue, comprising most of the animals commonly known as Polypes or Zoophytes, remains to constitute the modern Calenterata. 66 The Calenterata may be defined as animals whose alimentary canal communicates freely with the general cavity of the body ("somatic cavity"). The substance of the body is made up of two fundamental membranes—an outer layer, called the "ectoderm," and an inner layer, or endoderm." There are no distinct neural and hamal regions, and in the great majority of the members of the sub-kingdom there are no traces of a nervous system. Peculiar urticating organs, or “thread-cells," are usually present; and, generally speaking, a radiate condition of the organs is perceptible, especially in the tentacles with which most are provided. In all the Calenterata distinct reproductive organs have been shown to exist. The leading feature which distinguishes the Calenterata, and the one from which the name of the sub-kingdom is derived, is the peculiar structure of the digestive system. In the Protozoa, as we have seen, a mouth is only present in the higher forms, and in no case is there any definite internal cavity bounded by the walls of the body to which the name of "body-cavity" or "somatic cavity" could be properly applied (unless it be allowed that such really exists in the sponges). In animals higher than the Calenterata, on the other hand, there is not only generally a permanent mouth, but the walls of the body usually enclose a permanent chamber or "body-cavity." Further, in most cases, the mouth conducts into an alimentary canal, which is always distinct from the body-cavity, never opening into it, but usually passing through it to open on the surface by another distinct aperture (the anus). In most cases, therefore, the alimentary canal is a tube which communicates with the outer world by two apertures-a mouth and anusbut which simply passes through the body-cavity without in. any way communicating with it. In the Calenterata (fig. 29) Fig. 29.-Diagrammatic vertical section of a Sea-Anemone. a Mouth; s Stomach; Body-cavity; cc Convoluted cords ("craspeda ") containing thread-cells, and forming the free edges of the mesentery (m); t, t Tentacles; o Reproductive organ contained within the mesentery. The ectoderm (e) is indicated by the broad external line, the endoderm (e) by the thin line and the space between that and the ectoderm. there is an intermediate condition of parts. There is a distinct and permanent mouth, and a distinct and permanent bodycavity, but the mouth opens into, and communicates freely with, the body-cavity. In some cases (Hydrozoa) the mouth opens directly into the general body-cavity, which then serves as a digestive cavity as well (fig. 31). In other cases there intervenes between the mouth and the body-cavity a short alimentary tube, which communicates externally with the outer world through the mouth, and opens below by a wide aperture |