214 CCELENTERATA. 



attachment to solid surrounding objects in the sea. If the young 

 forms, which clitler from the sexual animal, gain the power of re- 

 producing by budding, the development leads to various forms of 

 alternation of generation. 



SUB-GROUPS. I. SPONGIARIA* = POEIFERA. 



The body has a sponyij consistence and is composed of masses of 

 cells capable of ameboid movements and supported by a solid, calcareous, 

 silicious, or horny skeleton. There are external pores, an internal 

 canal system, and one or many exhalent openings (osbula}. 



The sponges are at present universally regarded as Ccelenterata, 

 and in this group they are distinguished from the Cnidaria (Polyps 

 and Medusa?). They are composed of a contractile tissue, which 

 is usually supported by a framework composed of spicules and fibres ; 

 the whole being arranged in such a manner that there exists on the 

 external wall of the body larger and smaller openings ; and in the 

 interior a system of canals and spaces in which a continuous stream 

 of water is maintained by the vibratile motion of cilia. 



Amoeba-like cells, net-like membranes of sarcod^, flagellated cells, 

 spindle cells, ova, spermatozoa, and tissues 

 derived as excretions from cells are present 

 as the histological elements of the Sponge 

 body. The chief mass of the contractile 

 parenchyma is composed of the amoeba 

 like cells. These are granular cells, which, 

 like Amceb ^> have no external membrane, 

 can protrude and retract processes, and 

 f ake into their interior foreign substances (fig. 157). 



The framework or skeleton, which we find wanting only in the soft 



* Literature : Nardo G. D., " System der Schwamme," Isis, 1833 and 1834. 

 Grant, " Observations and Experiments on the Struct, and Funct. of Sponges," 

 Edin. Phil. Journal, 1825 1827. Bowerbank, "On the Anatomy and Physio- 

 logy of the Spongiadag," Pli'dos. Trans., 1858. and 18G2. Lieberkiilm, " Beitrage 

 zur Entwickelungsgeschichte der Spongillen," J\lilUc?'\t Arc-Mr., 1856. Lieber- 

 kiihn, " Zur Anatomic der Spongien," Mutter's ArcJtir., 1857, 1851), 1863, 1865, 



1867. O. Schmidt, " Die Spongicn des adriatischen Mceres," Leipzig, W. En g- 

 elmann, 1862, as well as Supplement. Leipzig, W. Engelmann, 18G4, 18(5(5, 



1868. E. Haeckel, "Die Kalkschwamme," 3 Bde, Berlin. 1872. FT. E. 

 Schulze, " Untersuchungen iiber den Ban und die Entwickelung der Spongiea," 

 Zeitiiclirlft,fiir vriss. Zool., 1876 1SSO. 



