PORIFERA 



21 



ectoderm and entoderm. Lastly, there occurs at the apical 

 ile an evagination of the bodj-wall like a chimney-pot, at 



Fig. 6.— Development of Osearella, diagrammatic (after Hkideb). A, swarming 

 blastula larva ; B, attached gastrula-stage ; C, stage initiating the closure of the 

 gastrula mouth (Gm) and the folding of the entodermic sac; D, young sponge ; Os, 

 oeculum po, inhalant pores ; Ec, ectoderm ; En, entoderm. 



