Neal. — Nervous Syst. Squalus. 



PLATE 2. 



All figures magnified 43 diameters and oriented as in Plate 1. The outlines 

 were first made from the translucent embryos with camera lucida, and afterwards 

 tlie embryos were studied as opaque objects. 



Fig. 4. An embryo with 4 somites viewed from the dorsal side. Locy's segments 

 are seen to be confined to the " marginal bands " of the cephalic plate. 



Fig. 5. An embryo with 10 or 11 somites viewed from the right side and parti}- 

 from above. The posterior part of the cephalic plate is seen to be 

 sharply flexed ventrad on the right side. 



Fig. 6. An embryo with 12 somites viewed from the right side. The neural folds 

 in the region of the cephalic plate have not yet met in the mid-dorsal 

 line. Tlie demarcation between cephalic plate and trunk is seen to be 

 sharp. The anterior three primary vesicles (encephalomeres I, II, and 

 III) appear in surface study as shown in the figure. In neither this 

 embryo nor in the one represented in Figure 6 do Locy's segments 

 appear. 



