PARAPHYSIS AND PINEAL REGION IN REPTILIA 369 



6. The three subdivisions of the fore brain and the two sub- 

 divisions of the niid brain presumably are secondary segments. 

 They do not seem to correspond exactly in structure with the 

 typical hind brain neuromeres and should therefore be distin- 

 guished from those segments which appear earlier and are essen- 

 tially primary neuromeres. 



7. In the lizard the paraphysis develops from one, two or 

 three primary outgrowths from the paraphysal arch. These ap- 

 pear first in embryos of 3.2-3.6 mm. The organ forms a long 

 tube with well developed tubules in its distal part and has a sort 

 of sinusoidal circulation. It is closely moulded over the dorsal 

 sack. 



In the turtle it develops from one outgrowth seen first in em- 

 bryos of about 6-7 mm. It becomes a relatively complicated 

 structure with many lateral tubules and a sinusoidal circulation 

 approaching that of amphibia. As in the lizard it grows back- 

 ward in close contact with the dorsal sack. 



8. The velum in both lizards and turtles forms only a slight 

 angle in early stages and is later much reduced towards the me- 

 dian line where it becomes a mere lip, which forms the caudal 

 boundary of the opening of the paraphysis. 



9. The post velar arch in the lizard forms a wide dome-like 

 dorsal sack which later becomes compressed to a high, deep trans- 

 verse slit. In the turtle the post velar arch forms an extensive, 

 vaulted dorsal sack which does not undergo that compression so 

 striking in the lizard. 



10. The pineal eye and the epiphysis of the lizard arise as two 

 outgrowths from the epiphysal arch, that for the eye being imme- 

 diately in front of that for the epiphysis. The outgrowths appear 

 in embryos of 2.4-3.6 mm. The pineal eye is separated from the 

 epiphysis in an embryo of 5 mm. and migrates gradually from the 

 region of the epiphysis to reach in final stages the parietal fora- 

 men. The epiphysis always remains attached to the brain bj'^ 

 an attenuated solid stalk and becomes much expanded distally. 

 It lies close against the caudal wall of the dorsal sack. In the 

 turtle there is no pineal eye. The epiphysis appears at 5 mm. 

 and becomes an elongated body with an expanded tip and rounded 

 stalk. It curves forward and lies over the dorsal sack. 



