534 LOCY. [Vol. XI. 



one set serving to fully corroborate the observations made on 

 the other. 



In Acanthias I have followed the history of these segments 

 very carefully, and have traced the earliest-formed ones zvith- 

 out a break into the later stages, and identified them with the 

 neuromeres. If, therefore, the segmental folds of the open 

 neural groove stage are artifacts, it may with equal force be 

 claimed that the so-called neuromeres, which are later stages of 

 the same segments, are also artifacts. 



It should also be borne in mind that similar segments exist 

 in correspondingly early stages in Amblystoma, Rana palus- 

 tris, Diemyctylus, and the chick. It is truly interesting to 

 observe the way in which these different kinds of material bear 

 out the interpretation, that we are dealing with veritable 

 anatomical structures. 



The most satisfactory reply to be given to the question is 

 based on study of fresh material. Fortunately, the chick offers 

 at all times a source where we can get living embryonic mate- 

 rial at any desired age, I have repeatedly observed these seg- 

 ments in living chick embryos ^ in the eighteen to twenty-two- 

 hour stages, and have treated them with reagents while they 

 were actually under observation. The effect of the addition 

 of picro-sulphuric acid is to render immediately the walls of the 

 neural groove opaque and more clearly defined, but not to affect 

 the number or arrangement of the segments. Camera sketches 

 have been made before the addition of the reagent and com- 

 pared with those made after the specimens were hardened. 

 The two correspond, as regards number and arrangement of 

 the segments. I have also noted these structures in living 

 embryos between the twelfth and fifteenth hours of incubation. 

 Their consecutive history has been traced in my laboratory by 

 one of my students, and the results may be expected to appear 

 later in this Journal. 



I have likewise observed them in living embryos of Amblys- 



1 The embryo was removed with a part of the blastoderm to normal salt solu- 

 tion, which was kept at the proper temperature, and the specimens tilted and 

 rotated with a very fine sable brush over a black background. The structures are, 

 of course, faint, and delicately, although definitely, outlined. 



