356 THE SPONGIDA OR PORIFERA. 



ciated together and embedded in a gelatinous material excreted by 

 themselves, the flagella and collars being the only parts projected 

 into the surrounding water. In the gelatinous bed of a colony of 

 Protospongia may be seen at the same time fully-developed collared 

 and flagellate monads, and monads with collars and flagella with- 

 drawn, some irregularly shaped and amoebiform, some dividing, 

 and yet others breaking up into spores. 



The glairy, tenacious sarcode of the Spongida corresponds 

 to the gelatinous bed of the colonised Infusoria, such as Proto- 

 spongia and allied genera. Distributed within this sponge sarcode, 

 or cytoblastema^ are numerous amoebiform cell-elements or cyioblastSy 

 which repeatedly change their form, move about from one part to 

 another of the sarcode, and by their action in the superficial or 

 peripheral layer of the latter (in which they are particularly abun- 

 dant) bring about the closing and opening of the pores and the 

 enlargement and diminution of the oscula. 



As in the colonised flagellate collared Infusoria, so in the 

 Spongida are the collared cells found to retract flagellum and 

 collar, some becoming amoebiform, sending out variously-shaped 

 pseudopodic extensions and moving about in the cytoblastema ; 

 others, again, either singly or after coalescence with other cells to 

 form larger bodies, assuming a quiescent state, then breaking up 

 by segmentation into rounded spores, which go to increase the 

 general sponge mass. "It is only requisite to point still more 

 emphatically," says Saville Kent, " to the fact that these spores, 

 distributed broadcast throughout the substance of the cytoblas- 

 tema, may, as ascertained by the author, be met with and traced 

 onwards through every intermediate size and stage, from the single 

 spheroidal spore up to the adult collared monads or amoebiform 

 cytoblasts ; the derivation of these spores through the splitting-up 

 into a granular or sporular mass of the entire substance of the 

 matured collar-bearing zooids being correspondingly substantiated." 

 The reproduction of the Spongida is effected, according to Saville 

 Kent's investigations, in a somewhat similar fashion. The collared 

 cells, with collars and flagella retracted, become amoebiform^ pass 

 into the cytoblastema, coalesce into larger ovoid bodies, divide by 

 segmentation into a swarm of ciliated or flagellate monads, in which 

 state this so-called "ciliated larva," or " swarm-gemmule," passes 



