160 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
the mesodermic somites in that region.” In the head region, where 
somites do not similarly press upon the neural plate, it still remains for 
Locy to show how structures morphologically dorsal, as his “neural 
segments” are, become converted into structures morphologically 
ventral as well as dorsal, as are the “hindbrain neuromeres,” for 
example. 
My own evidence of their continuity in time is, as I have said, nega- 
tive. Figure 4, Plate 2, represents an early stage with three or four 
somites. One sees the “marginal bands” of which Locy has spoken, 
but only the faintest traces of segments are visible. On one sido — 
the right — they are exceedingly irregular. At this stage the lateral 
edges of the neural plate are not flexed ventrally, and such segments as 
are to be seen at all show best from the dorsal side. A quite regular 
segmentation is seen on the left side of the cephalic plate, yet the seg- 
ments are by no means all of the same size or distinctness, nor do they 
equal in size the mesodermal segments. In the trunk region the lobes 
of the edge of the neural plate show no definite relation to the meso- 
dermal somites, the boundary between two somites coinciding in some 
cases with the depression between lobes, in others with the apices or 
with other parts of the lobes. I wish to call especial attention to the 
fact that here, as in the embryos shown on Plate 1, the segments are con- 
fined to the marginal bands, and therefore do not extend into the median 
plate. Here, again, there is a considerable discrepancy between Locy’s 
observations and my own. 
I have found it impossible: to trace definite segments into the later 
stages, for in these stages, before the closure of the neural tube, in the 
majority of specimens little or no evidence of segments along the cephalic 
plate can be seen, 
Two embryos in later stages of development are seen in Figures 5 and 
6, Plate 2. There is practically no evidence of segmentation or lobing 
of the edge of the medullary folds, The segments which Locy has 
numbered 1, 2, and 3 are visible in many specimens, in some very dis- 
tinctly, as shown in his photographs; but behind them there is an 
irregularly sinuous or entirely smooth edge, as shown in my Figures 5 
and 6, and in Locy’s photographic reproductions. These three anterior 
segments, according to Locy, shift their position. Since, however, 1 
do not find them constant in appearance and position, I have not been 
able to regard them as of morphological importance. It is worthy of 
note that they appear in the region of the neuropore, and that possibly 
they may be partly accounted for as the result of the difficulty of fusion 
