332 JOHN WARREN 



the walls of which are convoluted and enclose the paraphysis 

 between them. 



Fig. 23 shows the pineal region only of the brain of a turtle 

 32 mm., at a magnification of 110 diameters, in order to compare 

 this region more exactly with the larger lizards, as it is from 

 the largest turtle at my disposal. The paraphysis has a narrow 

 central cavity from which many lateral tubules are given off, 

 the whole organ now appearing as a very complicated glandular 

 structure. The walls of these tubules are closely related to vessels 

 as mentioned above, fig. 27. The walls consist of a single laj^er 

 of cells with large rounded or oval nuclei. The cell bounda- 

 ries are indistinct. The endothelial cells in the walls of the 

 vessels lie directly against the cells in the wall of the paraphysis. 

 We have here a sinusoidal arrangement very similar to that of 

 amphibia, Warren (97, fig. 20), but not so clearly developed. 

 The diencephalic plexus is essentially the same as in the previous 

 stage, though considerably more developed. The right half has 

 been mostly removed to give a better view of the left half. The 

 same is also true for the telencephalic and lateral plexuses which 

 however were not modeled. The epiphysis is much expanded 

 towards the apex and its outline a good deal distorted. It still 

 contains a cavity partially interrupted at intervals by incomplete 

 septa and has a solid hollow stalk. In structure it resembles the 

 epiphysis in the lizard. The commissures which are not shown 

 are the same as in the previous stages. In no specimen was there 

 any trace of Elliot Smith's commissure which was so striking 

 in Lacerta muralis. These last two stages are rather difficult to 

 compare with those of the older lizards. The older stage of 

 Chrysemys is probably very close to the final adult type. They 

 probably would fit in between the two oldest lizards, though as 

 regards the paraphysis and especially the plexuses the oldest 

 turtles studied show a development which seems more advanced 

 and complex than the adult lizard of fig. 13. 



