Herri CK, Brain of the Snake. 163 



sponsive development in the infundibulum. The cephalic sen- 

 sory epithelium remains as a continuous band along the palatal 

 surface's, but is thickened at the ridge bordering the mouth later- 

 ally, from which point it can be traced into the nasal epithelium. 



The remaining embryos at our disposal are from a black 

 snake killed July 19th. These seem to be relatively less devel- 

 oped than the last mentioned. (Plate XVI, Figs. 6, 7.) No 

 special description is necessary as the differences are all such as 

 may be explained as connected with the peculiarities of the 

 type. The above embryos will be referred to as E. I, E. II, 

 E. Ill, and C IV respectively. 



'Khe Dorsal Sensory Plate. — In reptilian embryos of 

 early stages the existence of a continuous sensory plate from 

 the hypophysis (pituitary) to the auditory region is very obvi- 

 ous. In very eaily stages the front of the embryo coincides 

 with the future infundibulum and the subsequent growth only 

 increases the dorsal surfaces without adding anything to the 

 ventral. The nasal sacs, lense capsule, and sensory epithelium 

 of the gill-clefts is one continuous plate differing from the re- 

 mainder of the ectoderm in its greater thickness and columnar 

 character. The epithelium has the proliferating power so char- 

 acteristic of the sensory epithelia and gives rise to its own gang- 

 lia and nerves. It would be natural to seek further homologies 

 in the lateral line organs. 



In embryos of Eutsenia of the age figured (Plate XVI, 

 Fig. I,) the olfactory pits are not formed but the dorsal sensory 

 plate is thickened cephalodorsad of the lense capsule. In Fig. i, 

 Plate XV, a portion of a section is shown which on the left side 

 illustrates the formation of the lense capsule but this section 

 does not show, what may be readily seen in others of the same 

 brood but less advanced, that the lense capsule epithelium is 

 continuous with another portion of the sensory plate of the 

 frontal region. Along the caudal regions this epithelium is 

 continuous with a thin membranous portion with flat cells. 

 Tracing this layer cephalad over the convexity of the primitive 

 vesicle it shows a tendency to thicken and to invaginate until it 

 fuses with the epithelium of the pituitary anlag. It seems to the 

 writer that there is no reason to doubt the suggestion that the 

 pituitary is that sensory invagination which is formed at the mor- 



