PHYLUM PORIFERA 



97 



body-wall. Both eggs and sperms occur in a single individual; 

 i.e. Grantia is monoecious or hermaphroditic. The development 

 of the fertilized egg has been observed in Sycon (Fig. 57) and is 

 probably similar to what occurs in Grantia. The egg (a) seg- 



Fig. 57. — Development of a simple sponge, Sycon. a, ovum; b, c, ovum 

 segmented; d, blastula; e, amphiblastula; f, commencement of invagination; 

 g, gastrula attached; h, i, young sponge. (From Parker and Haswell, after 

 Schulze.) 



