344 JOHN WARREN 



fig. 18. Here one sees clearly these three fore brain segments or 

 neuromeres, T, I. D, II. D. Figs. 32, 34 and 36 show a similar con- 

 dition in the snake, pig and sheep and are similar to KupfTer (57) 

 fig. 89, Neal (74) fig. 47, Acanthias, and Hill (42) fig. 42, Salmo 

 (see also Neumayer (75) figs. 6 and 7 for the sheep). 



Figs. 29, 31, 33, 35 and 37 are horizontal sections along the lines 

 A-B shown in the above parasagittal sections to show these fore 

 and mid brain segments in this plane. Compare with these Orr 

 (77) figs. 6 and 40, Uzard; McClure (67) fig. 9, chick; Herrick (39) 

 fig. 8, Eutaenia; Johnson (53) fig. 41, pig. 



The models, figs. 2-7 and 17-19 give a sagittal view of these 

 structures and may be compared with the following figures in 

 sagittal planes, Neal (74) figs. 19, 20, Acanthias; Kupffer (57) figs. 

 178-181, Salamandra, 215 Rana fusca, 239 Lacerta viridis, 240 

 Anguis fragilis, 246 Lacerta vivipara, 277, 278, 286, chick; Her- 

 rick (39) figs. 6 and 7, Eutaenia; Ziehen (100) figs. 47, rabbit, 

 and 66, sheep. 



As regards the number of mid brain segments, these are rather 

 apart from the subject of this paper which concerns chiefly the 

 fore brain. In the early models the mid brain has appeared as a 

 single simple segment. In fig. 17 turtle there seems to be a line 

 of subdivision into two segments. In the reptilia Orr found only 

 one mid brain neuromere while McClure found two. I should 

 think that if enough early stages were examined there might be 

 two segments or neuromeres here. Herrick in Eutaenia shows 

 the mid brain as a single vesicle. This seems to be the case in figs. 

 32 and 33, though there seems to be a hint here of a subdivision 

 in the mid brain. Figs. 34 and 35 of a pig show two distinct seg- 

 ments in the mid brain, as Johnson (53) has shown in his figs. 

 35, 36, 42. The same is seen in the sheep figs. 36 and 37. Zim- 

 mermann in the rabbit showed three mid brain segments and 

 Froriep three in the mole. Zimmermann finds three, McClure 

 two and Beraneck one in the chick's brain and McClure and 

 Waters each found two in Amblystoma. Kupffer describes five 

 in Salamandra, three inteleosts, Accipenser and Ammocoetes. It 

 is evident that there is a considerable difference of opinion as to 

 the number. I have given this brief resume of results because I 



