214 CCELENTEEATA. 



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

 forms, which differ 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*=:PORIFERA. 



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

 cells capable, of amueboid 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 (oscula). 



The sponges are at present universally regarded as Coelenterata, 

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

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

 is usually supported by a f ramework 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 sarcode, 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 arnceba- 

 like cells. These are granular cells, which, 

 FIG. 157. - Amoeba-like cell of like Anwebfe, have no external membrane, 



Spongilla. 



can protrude and retract processes, and 

 take into their interior foreign substances (fig. 157). 



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



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

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

 Edin. Phil Journal. 18251827. Bowerbank, " On the Anatomy and Physio- 

 logy of the Spongiadae," Pliilox. Trait*.. 1858 and 181)2. Lieberkiihn. " Beitrage 

 zur Entwickelungsgeschichte der Spongillen," Matter's Arcfi/i:, 1856. Lieber- 

 kiilm, " Zur Anatomic der Spongien." Mailer's Arcliir., 1857. 1859. 1863. 1865, 

 1867. 0. Schmidt, " Die Spongien des adriatischen Mceres," Leipzig, W. Eng- 

 elmann. 1862, as 'well as Supplement. Leipzig, W. Engelmanu. 1864, 1866, 

 1S68. E. Haeckel, "Die Kalkschwamme," 3 Bde, .Berlin. 1872. Fr. E. 

 Schulze, " Untersuchungeii iibcr den Bau und die Entwickelung der Spongien," 

 Zeitxelirift.fiir wiss. Zuol., 18761880. 



