472 B. F. KINGSBURY 
Chick. While in the chick embryo the brain plate is less clearly 
defined in the early blastoderm and the retinal foveae do not 
appear until after the neural folds have formed, fundamental 
agreement with the relations existing in the shark nevertheless 
exists. 
Despite the large amount of work done on the development of 
the chick, adequate descriptions of the early relations and trans- 
formations of the neural plate are lacking, and it was necessary 
to undertake a detailed study of a sequence of stages. Eighteen 
median plane reconstructions from sagittal sections were made 
by Mr. Adelmann and myself, of which six are here shown in 
accurate outline, but diagrammatically reproduced, as figures 12 
to 32. Of these, the reconstructions of figures 27, 29, 30, and 32 
were also utilized by Mr. Adelmann in his paper, who added 
four additional ones. 
Johnston (’09) does not describe the condition in the chick in 
detail, but it has been found that in this form as well as in the 
shark the primitive infundibular furrow is also a primitive optic 
furrow. ‘The earliest stage in which the furrow appears is one of 
six to seven somites (fig. 27). Here we see two slight furrows 
with equally slight prominences overlying a region where noto- 
chord mesoderm and entoderm are blended and intimately in 
contact (at least) with the neural plate. An earlier stage (four 
somites) illustrates the above-mentioned important characteris- 
tics of this important region without the presence of these fur- 
rows or slight depressions. There is an obvious pushing forward 
and downward of this region in the growth expansion. ‘The 
more anterior of these furrows becomes the primitive infun- 
dibular furrow, as may be seen by comparing figures 27, 28, 29, 
and 30. In the interval of development which they represent 
the optic vesicles have appeared, and by tracing the infundibular 
furrow to either side it is evident that it leads directly into those 
lateral expansions of the tube, fully substantiating Johnston’s 
interpretation. The community of relation of optic vesicle 
(furrow) and primitive infundibulum which exists in the interior 
of the tube has an external counterpart, as is well shown in the 
His models of the developing chick brain where optic vesicle and 
