104 THE ANATOMY OF INVERTEBRATED AXTMALS. 



Fig. li.—Ascetta primordialis (after Haeekel). 



I. A mature Astcetta^an of one side of the body of which is removed: 0, the exhal- 

 ent aperture ; p. iuhalent pores in the wall of the body ; i, endoderm ; e, ecto- 

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



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

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

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



III. A monadiform endodermal cell. 



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

 Amoeba. 



V. The cliiated embryo of Aacetta mirnbUis. 



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

 blastoccele. 



