324 JOHN WARREN 



arise a large number of tubules that are very closely applied 

 against the anterior wall of the post velar arch. The long 

 axis of the tube has changed its direction and now curves upward 

 and slightly forward, whereas in previous stages it curved up- 

 ward and backward and had a very sharp angle at about the 

 middle. The change in direction seems to be due to a backward 

 growth of the hemispheres, which in turn have forced the para- 

 physis and the anterior wall of the post velar arch backward 

 toward the posterior wall and have thus cooperated with the for- 

 ward growth of the mid brain in reducing this post velar region of 

 the diencephalon to a mere transverse slit. The upper part of the 

 slit is filled by the folds of the diencephalic plexus, which protrude 

 downward for a considerable extent into the cavity, fig. 15. This 

 compression of the upper part of the diencephalon with the sub- 

 sequent changes in the shape and relations of the parts is one of 

 the most striking features of the development of this part of the 

 lizard's brain. The pineal eye has now moved to its permanent 

 place in the parietal foramen. While the tip of the paraphysis lies 

 immediately below the vault of the skull the pineal eye is situ- 

 ated in its foramen at a considerable distance anterior to it. The 

 migration of the eye covers quite an extensive field. It is formed 

 at first from an outgrowth close to that of the epiphysis, both hol- 

 low and communicating by a sort of common opening with the 

 diencephalic cavity. It then separates from the epiphysis form- 

 ing a rounded hollow structure which rests against the epiphysis 

 and on the roof of the diencephalon. It next moves away from 

 the brain wall but remains in contact with the tip of the epiphysis 

 until it is finally separated from it by the extremity of the pa- 

 raphysis which is thrust in between them. Finally, after lying on 

 the dorsal aspect of the paraphysis it is carried forward to its final 

 resting place in the parietal foramen. During these moves its 

 shape gradually changes from a rounded vesicle to a circular disk 

 flattened from above downward. In only one stage have I been 

 able to see anything of a nerve for the eye; that was in the brain 

 of the 17.5 mm. embryo when a narrow band of tissue could be 

 seen passing from the eye downward, anterior to the epiphysis. 

 The staining of the specimens did not permit my following it to 



