104 THE ANATOMY OF IWERTEBRATED ANIMALS. 



Fig. 11. — Ascetta rtrimordiaiy (after Haecke!). 



I. A mature Ascetta, part of one side of the body of which is removed: 0, the exhal- 

 ent aperture : p. inhalent Dores in the wall of the body ; e, endoderm ; e, ecto- 

 derm ; q. ova. The triradiate spicula are seen imbedded in the ectoderm. 



II. A portion of the endoderm. with two pore? (p^; i. endcdermal cells— those round 

 the margins of the p-,res have their cilia directed inward ; e, ectodermal syncy- 

 tium; <7, ova ; z, sperm-cells. 



III. A monadif'orm endodermal cell. 



IV. An endodermal eel!, with retracted cilium, and having the characters of an 

 Arrmba. 



V. The ciliated emhrvo of Arcettn mimbiHs. 



VI. The same embryo in optical longitudinal section: e, epiblast : i, hypoblast ; v, 

 blastoccele. 



