PORIFERA 



21 



ectoderm and entoderm. Lastly, there occurs at the apical 

 pole an evagination of the body-wall like a chimney-pot, at 



Fig. 6.— Development of Oscarella, diagrammatic (after Heidee). 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, 

 osculum po, inhalant pores ; Ec, ectoderm ; Ea, entoderm. 



