Plate VI. 

 Details of Early Embryos. 



a. Arclienteron. 



(•(. Ectoderm. 



I///. Entoderm. 



,<'i. ,^'-''. First and second gill-clefts. 



//. Heart. 



K. Neurenteric opening, 



o/. Optic vesicle. 



/«. Pronephric region. 



?'. 2. Vitello-intestinal vein. 



Fig. 39- — Detail of embr3'o shown in plate i, fig. 35, viewed as an opaque object. 



Fig. 39 a-r. — Same embrj-o 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 iT. — Embryo shown in plate vi, fig. 38, viewed as an opaque object. 



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



184 



