CLASS I SPONGIAE 47 



iiicurrent canals with subdermal ciliated chambers, from which larger excurrent 

 canals conduct the water and food or excreta through the body, and generally 

 open into a wide, exhalent opening called the cloaca or paragaster. Stinging 

 cells, tentacles and radial mesenteries are absent. The Porifera comprise but 

 one class, the Sponges. 



Class 1. SPONGIAE. Sponges.^ 



Sponges are remarkable for their extreme variability in external form 

 and size ; they lead either an isolated existence, or are united in colonies of 

 cylindrical, tubulate, pyriform, fungus-like, bulbous, spherical, compressed, 

 foliate, umbel-, bowl- or beaker-shaped, or of botryoidal form. They are long- 

 or short-stemmed, or a peduncle may. be absent ; sometimes the stock is 

 branching, and the arms may be either separate or interlaced so as to form 

 networks. Nothing is less stable than the outer conformation, which varies 

 excessively according to the situation and other physical conditions, and 

 whose systematic importance, accordingly, is very slight. The size is also 

 extremely variable, ranging from that of a pin-head to 1| metres in diameter. 



Sponges are invariably sessile in habit, being attached either by means of 

 a stem or a bundle of anchoring spicules, or they may be simply encrusting 

 at the base. 



s- '■ The canal-system by which the whole body is traversed, is extremely com- 

 plicated in thick-walled, but simple in thin-walled sponges. A distinction is 

 recognised between incurrent or inhalent, and excurrent or exhalent canals. 

 In the terminology proposed by Rauff, inhalent canals are designated as 

 epirrhysa, and exhalent canals as aporrhysa ; the former terminate on the 

 periphery in ostia (not to be confounded with the finer dermal pores), while 

 the latter terminate on the cloacal surface in postica (again not to be con- 

 founded with gastral pores). Postica are usually larger than ostia, and 

 differ from them in form and arrangement. 



1 Literature : ^. Ou recent Sponges : — 



Schmidt 0.,Die Spougien des Adriatischen Meeres. Leipzic, 1864-66. — Idem, Die Spongien der 

 Kiiste von Algier. Leipzic, 1868. — Idem, Die Spougien des Meerbu&ens von Mexico. Jena, 1879-80. 

 — Haeckel, E., Die Kalkschwiimme, 1872. — Schulze, Fr. E., Untersuchungeu liber den Bau 

 und die Entvvicklung der Spongien. Zeitschr. f. wiss. ZooL, 1876-80, vols, xxvii. - xxx. — 

 Report on the Hexactiuellida. Scieut. Results Challenger Exped., Zool., vol. xxi., 1887. — 

 Vosmaer, G. G. J., Spongien {Porifera), in Bronn's Classen und Ordnungen des Tierreichs, 

 2nd ed., 1882-87, vol. iii. — Lendeiifeld, R., A Monograph of the Horny Sponges. London, 1889. 



B. On fossil Sponges : — 



Gold/uss, A., Petrefacta Germaniae, vol. i., 1826-33. — Michelin, H., Iconographie zoophyto- 

 logique, 1840-47. — -Fromentel, E. de, Introduction a I'etude des t'ponges fossiles. Mem. Soc. Linn. 

 Normandie, 1859, vol. xi. — Roemer, F. A., Die Spongitarien des norddeutschen Kreidegebirges. 

 Palaeontographica, 1864, vol. xiii. — Zittel, K. A., Ueber Coeloptychium. Abhandl. k. bayer. 

 Akad., 1876, vol. xiii. — Studien iiber fossilen Spongien, i., ii., iii., ibid., 1877, vol. xiii. (translated 

 by Dallas in Annals and Mag. of Nat. Hist, for 1877, 1878, 1879). — Beitriige zur Systematik der 

 fossilen Spongien, i., ii., iii., Neues Jahrb. fvir Mineral. 1877, 1878, 1879. — Quenstedt F. A., 

 Petrefacteukunde Deutschlands, 1877, vol. v.—Sollas, W. J., Quart. Journ. Geol. Soc. 1877-80, 

 vols, xxxiii. - xxxvi. — Rinde, G. J., Catalogue of fossil Sponges of British Museum, London, 

 1883. — Monograph of British fossil sponges ; Palaeontographical Society, 1887, 1888, 1893. — 

 Rauff, H., Palaeospongiologie ; Palaeontographica, 1893 - 94, vols, xl., xli. (contains full 

 bibliography). — Schrammen, A., Beitrag zur Kenntniss der obersenonen Tetractinelliden. Mittheil. 

 Roemer. Museum Hildesheim, 1899-1903, Nos. 10, 14, 15, 19.— Hall, J. and Clarke, J. M., 

 A Memoir on the Palaeozoic reticulate Sponges constituting tl^e family Dictyospongidae. N. Y. 

 State Mus. Mem. ii., 1898. Earlier contributions by same authors in 15th and 16th Reports N. Y. 

 State Geologist, 1895-96. — Schrammen, A., Kieselspongien der oberen Kreide von Nordwestdeutsch- 

 land. Palaeontogr. 1910, Supplem. vol. v. — Kolb, R., Kieselspongien des schwabischen weissen 

 Jura. Oj). cit., 1911, vol. Ivii. 



