104 THE ANATOMY OF INVERTEBRATED ANIMALS. 



HI 



FIG. ll.Ascftta rrrimordialif (after Haeckel). 



I. A mature Ascertain of one fide of the body of which is removed: 0, the exhal- 

 ent aperture ; p. inhalent ooree in the wall of the body ;.f, endoderm ; r?, ecto- 

 derm ; 7, ova. The triradiate spicnla are seen imbedded in the ectoderm. 



II. A portion of the endoderm, with two pores (p}\ i, endcdermal cells those round 

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

 tinm: g, ova ; z, sperm-cell*. 



m. A monadiform enflodermal cell. 



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

 Amoeba. 



V. The cliiated emhryo of Afcett.fi mirnbUfs. 



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

 blastoccele. 



