CLASS I SPONGIAE 47 



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curreiit canals with subdermal ciliated Chambers, from which larger exciirrent 

 nals coiiduct the water and food or excreta through the body, and generally 

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

 11s, tentacles and radial mesenteries are absent. The Porifera comprise but 

 one class, the Sponges. 



Olass 1. SPONGIAE. Sponges.i 



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, fungns-like, bulbous, spherical, compressed, 

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

 or short-stemraed, 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 aecording 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 J metres in diameter. 



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

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

 at the base. 



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. 



^ Literature : ^. On receut Sponges : — 



Schmidt O., Die Spoiigien des Adriatischen Meeres. Leipzic, 1864-66. — Ide7)i, Die Spongien der 

 Küste von Algier. Leipzic, 1868. — Idem, Die Spongien des Meerbusens von Mexico. Jena, 1879-80. 

 — Haeckel, £., Die Kalkschwämme, 1872. — Schulze, Fr. Iß., Untersuchungen über den Bau 

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

 Report on the Hexactinellida. Scient. Results Challenger Exped., Zool,, vol. xxi., 1887. — 

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

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



B. On fossil Sponges : — 



Ooldfuss, A., Petrefacta Germaniae, vol. i., 1826-33. — Michelin, H., Iconographie zoophyto- 

 logique, 1840-47. — Fromentel, E. de, Introduction ä l'etude des eponges 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 über fossilen Spongien, i., ii., iii., ibid., 1877, vol. xiii. (translated 

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

 fossilen Spongien, i,, ii,, iii., Neues Jahrb. für Mineral. 1877, 1878, l^l^.—Quenstedt F. A., 

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

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

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

 Rmtff, H., Palaeospongiologie ; Palaeontographica, 1893-94, vols. xl., xli. (contains füll 

 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 the family Dictyospongidae. N. Y. 

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

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

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

 Jura. Op. dt., 1911, vol. Ivii. 



