Herrick, Brain of the Snake. i6i 



ours had three perforate and one cleft which may not have been 

 perforate. This stage was secured in Granville, O., June 9th. 

 Plate XVI, Fig i, shows the general appearance while Fig. 2 is 

 an enlarged drawing of the head (camera outline.) The eye 

 is in a primitive condition, the lense capsule still cohering with 

 the skin and unclosed. The cervical flexure is more than 45 

 degrees, the mesencephalic flexure more than 90 degrees. 

 The diencephalon is still much longer and larger than 

 the primary prosencephalic vesicle. The nasal sacs have not 

 yet formed and the olfactory epithelium is connected with the 

 hypophysis anlag and lense capsule by a continuous band of 

 sensory epithelium. The point on the ventral surface where the 

 great mesencephalic flexure is pivoted is obviously the angle of 

 the jaw, or the region of the hypophysis (pituitary.) Rathke 

 is correct in saying that the latter body is not as yet formed, but 

 its anlag as a thickened patch of epithelium is quite obvious. 

 Plate XIX, Fig. i, (207.5.) The recognition of the region of 

 the hypophysis as the morphological front of the head serves to 

 interpret for us several of the most difficult problems of com- 

 parative morphology. The morphological front of the brain is 

 the region of the infundibulum, from which the true terma may 

 be traced cephalo-dorsad. The diverticles beyond this point 

 are all from the dorsal or dorso-lateral aspects of the brain. 

 These may be counted as follows : recessus opticus, primary 

 prosencephalic vesicle, dorsal sac, epiphysis, and roof of the 

 thalamus proper. If this interpretation could be accepted, the 

 prce-commissura, callossum, hippocampal commissure, habena 

 and supra-commissures, are all analogous structures. The sen- 

 sory epithelium of the forehead region gives rise to (i) hypophy- 

 sis, (2) Jacobson-nasal structure, (3) lense capsule. It is pos- 

 sible that the latter belongs to the epidermal area corresponding to 

 the mesencephalon and that it has been excentrically displaced 

 by the rapid arching of the head. We would recognize the e.x- 

 istence of a lateral sensory epithelium band which is strictly 

 lateral in the post-cephalic regions and becomes symmetrically 

 segmental forming the lateral line system. In the region of the 

 gill clefts this system gives rise to the branchial sensory organs. 

 Cephalad of this point the strong and irregular growth and flex- 

 ures serve to disarrange the primitive simplicity of the epithe- 



