458 Leland Griggs 



This group of four neuromeres constituting the procephalic 

 lobes 's further marked off from the rest of the plate by its height 

 (fig. 5, D; Plate I, figs. 11, 12), and also by its darker color as in 

 previous stages. These distinctive characters make it convenient 

 to apply the term 'Hagma" suggested by Lankester for a more 

 or less isolated and independent group of segments. The aptness 

 of this term will become more apparent as the development of 

 the procephaic lobes is followed in the succeeding stages and 

 when it is discussed in the conclusion. 



It has already been noted in this paper that there are few 

 observations of neuromeres present in the open neural plate. 

 Kupffer ('93) found six or seven neuromeres in the expanded 

 end of the plate of Salamandra atra. Froriep ('91, '93,) found 

 in the same region of Triton five neuromeres and in Salamandra 

 four, but he later denied their real metameric value. Locy 

 ('95) found a few large divisions in the cephalic plate of Ambly- 

 stoma and in the plate of Rana palustris which, however, he 

 did not regard as true neuromeres. Eycleshymer ('95) found 

 divisions in the neural plate of Amblystoma which he regarded 

 as artifacts. Hill ('00) found in the anlage of the combined 

 forebrain and mid-brain of the trout and the chick five neuro- 

 meres. Although these authors differ as to the number of 

 segments that shall be assigned to the brain region of the neural 

 plate and although they fail to agree as to the meaning of the 

 segments, yet the evidence taken as a whole is strongly in favor 

 of the presence of true neuromeres in the open neural plate. 

 The cause of disagreement, particularly as to the number of 

 segments, seems to be the lack of landmarks. The broad anterior 

 end of the neural plate cannot be traced directly into a well 

 defined region of the brain without some such boundary as the 

 transverse cephalic groove. Kupffer admitted that he was 

 unable to find such a landmark in Salamandra. Locy used the 

 entire expanded portion of the plate as forming in a general 

 way the anlage of the brain. Hill is the only author who has 

 yet described anything corresponding to the transverse cephalic 

 groove of Amblystoma. He found that in the solid anlage of 

 the trout brain there were two deep '^dorsal grooves" one in 



