Plate VI. 

 Details of Early Embryos. 



Archenteron. 



Ectoderm. 



Entoderm. 



First and second gill-clefts. 



Heart. 



II. Neurenteric opening. 



op. Optic vesicle. 



/;/. Pronephric region. 



7'. z. Vitello-intestinal vein. 



Fig. 39. — Detail of embryo shown in plate i, f\g. 35, viewed as an opaque object. 



Fig. 39 a-i\ — Same embryo viewed in various positions as transparent object. 



Fig. 40. — Embryo shown in plate vi, fig. 36, viewed as a transparent object. 



Fig. 41. — Embryo shown in plate vi, fig. 37, viewed as a transparent object. 



Fig. 41 a. — Embryo shown in plate vi, fig. 38, viewed as an opaque object. 



Fig. 41 l>. — Embryo shown in plate vi, fig. 38, viewed as a transparent object. 



184 



