48 



INVERTEBRATA 



CHAP. 



which is the centre for the formation of the gemmule. Here they 

 become massed together so as to form a spherical lump. Other 

 wandering cells with less yolk follow after them and form a layer 



I 



cent 



FIG. 25. Longitudinal sections of Amphiblastula larva, just fixed larva, and young 

 sponge of Leucosolenia variabilis. (After Minclriu.) 



A, free-swimming larva. B, just iixed sta-c. C, young sponge four days old ; cent, central cells ; 

 fl, flagellated cells ; </;-, granular cells ; int, intermediate cells : I, lens ; j,i<j, pigiaeuted cells. 



surrounding them, in which the individual cells, as a consequence of 

 mutual pressure, assume a columnar form. The investment is for a 

 considerable time not quite complete, and an opening therefore exists. 

 In this opening are found some specially large cells called tropho- 



