No. 3-] THE VERTEBRATE HEAD. 511 



He also recorded the presence of neuromeres in Amblystoma 

 embryos with wide open neural groove, but differs from Kupffer 

 in locating them in the neural ridges instead of the median 

 neural plate. (See further on this point, p. 530.) 



From the foregoing historical survey it appears that our 

 knowledge regarding metamerism in the neural tube has passed 

 through the phase of simple observation of its occurrence (Von 

 Baer, '28, Remak, '50, Dursy, '69, and others), and has grown 

 by successive additions to the recent conception of its seg- 

 mental importance. In reaching this point, first came the work 

 of Beraneck ('84) and Orr ('87), showing that the neuromeres of 

 the hind-brain are definitely connected with nerves; following 

 this it was demonstrated by Kupffer, partly, in 1886, and by 

 McClure, definitely, in 1889, that the neuromeres extend 

 throughout the neural tube, and that those of the trunk region 

 merge gradually into those of the head region. Lastly, the 

 neuromeres of the mid-brain have been especially studied by 

 Waters (-92), the condition of that brain region having been 

 left undetermined by previous observers. Remak was the first 

 (1850) to suggest the segmental relations of nerves and neural 

 segments; Beraneck the first (1884) to demonstrate it. From 

 this time onward the definite relation of nerves and neuromeres 

 began to be studied, and both Orr ('87) and Hoffmann ('88) are 

 pioneers in this line of study. 



It will be observed that previous to the appearance of my 

 paper just referred to, no one but Kupffer and Froriep had 

 claimed a very early appearance for neural segments, and these 

 two authors had recorded their appearance only in the median 

 part of the neural plate, and not in the neural ridges. They 

 had not shown the structures of the open neural groove stage 

 to be in any way connected with the neuromeres of later 

 periods, which are present in the lateral walls of the neural 

 tube. 



In the case of Froriep's observations I think there is reason 

 to doubt whether the segments observed are really the " neural 

 segments " of other writers. The small number (4 or 5) which 

 he observed in the head region does not correspond with the 

 number of neuromeres observed by any other author in the 



