334 JOHN WARREN 



surface of the neuromere while the nuclei lay nearer the outer 

 surface and approached the inner surface only at each end. The 

 cells of one did not pass over into an adjacent neuromere and the 

 cells between each pair were so crowded together that they 

 formed a sort of septum between each neuromere. The five 

 hind brain neuromeres all showed these features. He regarded 

 the mid brain as one neuromere and between this and the second- 

 ary fore brain were two whose structure however was not quite 

 the same as those in the mid brain and therefore he did not regard 

 them as true neuromeres. His fig. 6, pi. 12, and fig. 40, pi. 

 15, show the secondary fore brain or telencephalon; then follow 

 two well marked neuromeres and behind them the mid brain. 

 These figures are essentially the same as figs. 29 and 31 and 37. 

 Orr's fig. 63, pi. 16, shows the fore brain in sagittal section and 

 corresponds to fig. 8, Lacerta muralis, 4.5 mm. Here the pos- 

 terior commissure is seen occupying a part of the intercalated 

 portion of the diencephalic roof. Hoffmann (50) as a result of ob- 

 servations on reptilian embryos agrees essentially with Orr, 



McClure (66, 67) studied Amblystoma, lizard and chick. He 

 divided neuromeres into myelomeres or constrictions of the mye- 

 lon and encephalomeres or constrictions of the encephalon. 

 He found in the hind brain five encephalomeres in Amblystoma 

 and six in the chick. In the mid brain there were two. To these 

 he gave the name of oculomotor and trochlear neuromeres. In 

 the fore brain he saw two, which he named the olfactory and optic 

 neuromeres and also traces of a third. He observed a similar 

 condition in the newt and chick, and states that these forebrain 

 neuromeres are true neuromeres as far as their external character 

 and structure are concerned. As regards the third fore brain 

 neuromere this appeared just in front of the mid brain It was 

 smaller than the others and McClure expressed doubts about its 

 neuromeric value. This segment is doubtless the synencephalic 

 neuromere of KupfTer. McClure's (67) fig. 9 shows the condition 

 in the chick and corresponds to figs. 29, 31, 35 and 37. His 

 II N. M. is the second diencephalic, and the I A^. M. the first 

 diencephalic neuromere as shown in my models figs. 3, 4, 17, and 

 18, and in the figures just mentioned. 



