THE SPONGES 



213 



in the autumn just before the death of the- adult sponge. In the 

 spring they develop into new sponges. They are of value in 



I I 



a * * 



II 1 



FIG. 128. Types of canal systems of sponges. 



A, ascon type; B, sycon type; C, rhagon type. The arrows indicate the 

 direction of the current of water. The thick black line in A and B represents the 

 gastral layer ; the dotted portion, the dermal layer. 



ap.p, apopyle ; fl.c, flagellated chamber ; GC, gastral cavity (cloaca) ; in.c, in- 

 current canal ; osc, osculum ; pr.p, prosopyle ; C, flagellated chambers ; DP, 

 dermal pores ; Ex, excurrent canals ; GO, openings of excurrent canals ; In, in- 

 current canals; O, osculum; PG, gastral cavity; SD, subdermal cavity. (From 

 Minchin.) 



carrying the race through a period of adverse conditions, such 



as the winter season. Only a few sponges reproduce in this way. 



Grantia. A sponge slightly more complex than Leucoso- 



lenia is Grantia (Fig. 127, C). Grantia also lives along the coast 



