PLATE VI. 

 DETAILS OF EARLY EMBRYOS. 



a. Archenteron. Neurenteric opening. 



ec. Ectoderm. of. Optic vesicle. 



fill. Entoderm. / Pronephric region. 



ffi. g- n . First and second gill-clefts. v. i. Vitello-intestinal vein. 



A. Heart. 



Fig. 39. Detail of embryo shown in plate i, fig. 35, viewed as an opaque object. 



Fig. 39 a-e. 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 b. Embryo shown in plate vi, fig. 38, viewed as a transparent object. 



184 



