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.! 
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 e, accordingly, is very slight. The size is also extremely variable, 
ranging from that of : a pin-head to 1h 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.” 
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, O., Die Spongien des Adriatischen Meeres, Leipzig, 1864-66.—Die Spongien des 
Meerbusens von Mexico, Jena, 1879-80.—Hoaeckel, H., Die Kalkschwaimme, 1872.—Schulze, F. £., 
Untersuchungen iiber den Bau und die Entwickelung der Spongien ; Zeitschr. fiir wissenschaft. Zool., 
Bd, XXVII., XXVIII, XXX., 1876-80.—Report on the Hexactinellida; Sci. Results Challenger 
Exped., Zoology, vol. XXI. 1887.—Vosmaer, G. C. J., Porifera; Bronn’s Classen und Ordnungen des 
Thierreichs (2nd ed.), Bd. TI. 1882-87.—Lendenfeld, R. v., Das System der Spongien ; Biolog. 
Centralblatt, Bd. [X. 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, ie ‘tion a l'étude des éponges fossiles ; Mem. Soc. Linn. Normandie, 
vol. XI. 1859. — Roemer, F. , Die Spongitarien des norddeutschen Kreidegebirges ; Palaeonto- 
graphica, Bd, XIT. 1864. Fitted kK. A., Ueber Coeloptychium ; Abhandl. k. bayer, Akad. Bd. XII. 
1876.—Studien iiber fossile Spongien, I., IT., III., ‘béd. Bd. XIII. 1877 (translated by Dallas in Annals 
and Magazine of Nat. Hist. for 1877, 1878, 1879).—Beitriige zur Systematik der fossilen Spongien, 
I., IL., II. ; Neues Jahrb. fiir Mineral. 1877, 1878, 1879.—Quenstedt, F. A., Petrefactenkunde 
Deutschlands, Bd. V. 1877.-—Sollas, W. J., Quart. Journ. Geol. Soc. vol. XX XIII. 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.—Rauff, H., Palaeospongio- 
logia ; Palaeontographica, Bd. XL. 1893. 
2 [In the terminology proposed by Rautf (tom. cit.), inhalent canals are designated as epirrhysa, 
and exhalent canals «porrhysa ; 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. | 

