174 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY, 
compared by him with the ‘‘neuromeres” of the medulla.? Such sym- 
metrical cross furrows on the widely expanded neural plate of embryos 
of Salamandra atra were described by Kupffer ('86), and considered by 
him as remnants of a primitive segmentation. Since Kupffer believed 
that at this stage there was no trace of mesodermic somites, he regarded 
the segments as “primary,” i. e. not formed secondarily in adaptation to 
the mesodermal segmentation. Both Froriep (’92) and Wiedersheim (92) 
have, however, declared that mesodermal somites are present at the stage 
described by Kupffer, and that the segments could be explained as the 
passive result of the pressure of these somites. Locy (’95) finds in the 
trunk region of embryos of S. acanthias with a widely expanded cephalic 
plate that the lines of division between his “neural segments” may be 
traced inward toward the median furrow, probably as the result of the 
appearance of somites in that region. As stated on page 160, I have 
failed to find this exact correspondence between the neural segments 
of Locy and the somites. 
When the neural plate has closed to form the neural tube, the regions 
of elevation between the furrows become constrictions, which however 
affect only the ventral half of the tube, i. e. that portion against which 
the somites lie (see Fig. 41, Plate 6). Neither frontal sections nor 
cleared specimens give evidence of constrictions in the dorsal half of the 
tube, The constrictions in the ventral half of the tube are most clearly 
marked in the early stages, when the mesodermal somites are most rounded 
in form, and they disappear as this rounded form disappears.” 
Figure 39, Plate 6, represents a frontal section in the ventral half of 
the myelon of an embryo with 28-30 somites (Balfour's stage H). The 
right half of the neural tube and of the mesoderm is shown. It is seen 
that the wall of the neural tube shows a rounded constriction opposite 
the somite, while opposite the cleft between two somites, and conform- 
ing with it, an outer ridge and an inner rather sharp groove are seen. 
This section affords evidence more favorable to the contention that 
“ neuromeres” exist in the spinal cord than that seen at any other stage 
of development, or in any other plane of sectioning. In dorsal sections 
of the same series the constrictions disappear, as do the somites also. 
1 Marshall (’78) had previously stated that in the chick “the cord is slightly 
constricted opposite the centres of the protovertebre, and slightly dilated opposite 
the intervals between successive protovertebra.” 
2 Miss Platt (’89) has said with regard to the chick, “ Here [in the trunk region] 
as in the medulla, the segmentation is more manifest in the ventral region than in 
the dorsal.” 
