42 COELENTERATA PORIFERA SUB-BRANCH i 



of water laden with food-particles. The pores communicate by means of fine 

 incurrent canals with sub-dermal ciliated chambers, from which larger excurrent 

 canals conduct the water and sponge-food 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. 1 



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, leaf- 

 like, 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 J 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. 



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. 2 

 The water enters through the dermal pores, and passes through the incurrent 

 canals into the ciliated chambers, which are lined with epithelial cells. From 

 these it is conveyed through all parts of the body by means of the frequently 

 branching excurrent canals, which open into a sac-like, tube-like, or funnel- 

 shaped cloaca. The exhalent opening of the latter is termed the osculum. 

 Extremely thin-walled sponges have no cloaca, osculum, or branching canal- 



1 Literature : A. On recent Sponges. 



Schmidt, 0., Die Spongien des Adriatischen Meeres, Leipzig, 1864-66. Die Spongien des 

 Meerbusens von Mexico, Jena, 1879-80. Haeckel, K, Die Kalkschwamme, 1872,Schulze, F. K, 

 Untersuchungen iiber den Ban und die Entwickelung der Spongien ; Zeitschr. fur wissenschaft. Zool., 

 Bd, XXVII., XXVIII., XXX., 1876-80. Report on the Hexactinellida ; Sci. Results Challenger 

 Exped., Zoology, vol. XXI. 1887. Vosmaer, G. O. J., Porifera ; Bronris Classen und Ordnungen des 

 Thierreichs (2nd ed.), Bd. II. 1882-87. Lendenfeld, Jl. v., Das System der Spongien ; Biolog. 

 Centralblatt, Bd. IX. 1889. A Monograph of the Horny Sponges, London, 1889. 



B. On fossil Sponges. 



Goldfuss, A., Petrefacta Germaniae, Bd. I. 1826-33. Michelin, H., Iconographie zoophytologique, 

 1840-47. Fromentel, E. de, Introduction a 1'etude des eponges fossiles ; Mem. Soc. Linn. Normandie, 

 vol. XI. 1859. Moemer, F. A., Die Spongitarien des norddeutschen Kreidegebirges ; Palaeonto- 

 graphica, Bd. XII. l&(M.Zittel, K. A., Ueber Coeloptychium ; Abhandl. k. bayer. Akad. Bd. XII. 

 1876. Studien iiber fossile Spongien, I., II., III., ibid. Bd. XIII. 1877 (translated by Dallas in Annals 

 and Magazine of Nat. Hist, for 1877, 1878, 1879). Beitrage zur Systematik der fossilen Spongien, 

 I., II., III.; Neues Jahrb. fur Mineral. 1877, 1878, 1879. Quenstedt, F. A., Petrefactenkunde 

 Deutschlands, Bd. V. l877.Sollas, W. /., Quart. Journ. Geol. Soc. vol. XXXIII. 1877, and XXXVI. 

 1880. Hinde, G. J., Catalogue of fossil Sponges of British Museum, London, 1883. Monograph of 

 British fossil Sponges ; Palaeontographical Society, 1887, 1888, 1893. Ran/, H., Palaeospongio- 

 logia ; Palaeontographica, Bd. XL. 1893. 



'-' [In the terminology proposed by Rauff (torn, cit.\ inhalent canals are designated as epirrhysa, 

 and exhalent canals 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 confounded with gastral pores). Postica are usually larger than ostia, and differ from them in 

 form and arrangement. TRANS.] 



