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 



0, 

 esc. A 



*W ~"^ *r-'\* 1 ^^ 



v*. 



We. 



B 



o. p , c 



CO 



DP 



In 



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 Leueoso- 



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



