104 THE iiNATOMT OF IXVERTEBRATED AmifALS. 



Fio. 'il.—Ascfiffa vrimorcUalis (after Ilaecke]). 



I. A mature Asceffa, Tpart of one side of the body of which i? removed: o, the exhal- 

 ei)t aperture ; p. inhnleut pore? in the wall of the body ; i, endoderm ; <?, ecto- 

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



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

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

 tium: (7, ova ; z, sperm-cells. 



ITT. A monadiform endodermal coll. 



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

 Ammbn. 



V. The ciliated emhryo of A'cetfa mirrrbUh. 



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

 blastocoele. 



