474 Leland Griggs. 



find some morphological reason for the peculiar character of 

 the mid-brain. Johnston ('05) suggests that at the anterior 

 end of the nervous system there is included in the brain an 

 ''area which at the level of the acustico-lateral anlage is supposed 

 to be left out." It has certainly, however, never before been 

 demonstrated that the peculiar structure, the optic lobe, lies 

 originally external and lateral to the neural axis. 



From this history of the anlage of the lateral eyes and their cen- 

 ters, the optic lobes, it might be expected that the anlage of the 

 parietal eyes could also be found near the open neural plate. Locy 

 ('95) has claimed to have found them in the embryos Squalus as 

 a series of ''accessory optic vesicles" lying behind the true optic 

 vesicles of the lateral eyes. Hill ('00) has confirmed the presence 

 of these accessory optic vesicles in his study of the chick. Nothing 

 of this kind however seems to appear in Amblystoma. The 

 pineal eye forms very late. No new facts could be discovered 

 either in support or in refutation of Locy's theory. 



The post-cephalic region at the time the neural crests close 

 over presents a very characteristic appearance due to the presence 

 of narrow shallow grooves running across the plate transversely 

 and obliquely in no regular pattern (fig. 8, A). This is one more 

 factor which aids in marking off the procephalic lobes from the 

 remainder of the plate. 



Stage 9 (fig. 12). A few figures of older embryos are intro- 

 duced here in order to carry the work to a point where the more 

 important landmarks of the adult brain may be readily recog- 

 nized. Fig. 12, B and C, are side views of embryos just old 

 enough to show the otic pit (op) and the swellings of the brain 

 tube called by Kupffer secondary neuromeres. The changes 

 that take place between the closing of the neural tube and the 

 condition represented by these older embryos are readily 

 understood. Fig. 12, A, is a view of an embryo in which the 

 neural crests have already fused. The optic vesicle is divided 

 by a faint groove or constriction into eye stalk (es) and eye 

 vesicle proper (e) . The mid-brain is bilobed as in the preceding 

 stage (mbl, mb2). The cerebellar swelling (ml) now begins 

 o separate a little from the neural crest. A series of new swell- 



