PARAPHYSIS AND PINEAL REGION IN REPTILIA 335 



In McClure's fig. 8a there is seen the trace of a tMrd dience- 

 cephahc neuromere on one side only as the section is quite oblique. 

 I have found nothing to compare with it, my results correspond- 

 ing with his fig. 9. The optic neuromere has no nerve connected 

 with it as the optic nerve is secondary in character and is not 

 reckoned as one of the segmental nerves. He suggests that the 

 primitive segmental nerve which belongs here has degenerated. 

 The olfactory nerve of course belongs to the first neuromere. 

 He concludes that ''the encephalomeres are not only remnants 

 of neural segments similar to the myelomeres, but that they were 

 originally continuous." 



Waters (98) made his investigations on the cod and Ambly- 

 stoma. His results in the latter were more satisfactory than in 

 the former. He found here three neuromeres in the fore brain 

 and two in the mid brain. Zimmermann (101) studied Mustelus, 

 chick and rabbit embryos. He found eight neuromeres at the 

 time of closure of the neural tube. The three anterior corre- 

 sponded to the fore, mid and hind brain vesicles. The five poste- 

 rior belonged to the medulla. The fore brain divided secondarily 

 into two, the mid brain into three and the hind brain into three 

 neuromeres. He gave to these secondary subdivisions full meta- 

 meric value. His observations on the fore brain and mid brain 

 therefore gave five neuromeres to these regions which corresponds 

 to McClure, Waters and von Kupffer. 



Herrick (39) studied the brain of the snake, Eutaenia. His fig. 

 8, pi. 19, shows a horizontal section through telencephalon, two 

 diencephalic neuromeres and a part of the mid brain. Compare 

 this with McClure, fig. 9, Orr, fig. 6 and 40 and my figs. 29, 31, 33, 

 35 and 37, Herrick's figs. 6 and 7 sagittal show the three fore 

 brain subdivisions as they appear in my figs. 7 and 18. He criticizes 

 Waters, Zimmermann and McClure for having tried to homologize 

 dorsal expansions in the fore brain with ventral expansions in the 

 mid and hind brains. ''If neuromeres once existed in the fore 

 brain they would be only visible at an early stage and would be 

 obscured by altered conditions. The so-called fore brain neuro- 

 meres differ from those in the medulla and cord in involving only 



