104 THE ANATOMY OF INVERTEBRATED ANIMALS. 



Fig. n.—Ascpffa vrimordiaUf: (after Haccke]). 



I. A mature /(yce«r/,parf of one side of the horly of which i? removed: o, the exhal- 

 ent aperture ; ;;. inhalent pore? in the waH'of the body ; e, endoderm ; ^, ecto- 

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



II. A portion of the endoderm. with two pores (p^; i. endodermal cells— those round 

 the mari^iuB of the pores have their cilia directed inward ; f, ectodermal syncy- 

 tium: 0. ova : 2, sperm-cells. 



ITT. A monad! form endodermal cell. 



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

 Amcehn. 



V. The ciliated embryo oi AfcHta mirnhilJR. 



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

 Dlastoccele. 



