636 The American Naturalist. [August, 
the formation of nervous matter, but that some of it became 
mesenchymatous and was possibly utilized in the development 
of the skeleton. Other authors at about the same time con- 
firmed more or less clearly this view that all mesenchyme was 
not of entodermal, but that at least some of it was ectodermal, 
in origin. 
In 1893, Miss Julia B. Platt, in a preliminary paper, made 
the noteworthy statement that the embryology of Necturus 
showed that, at least in the head, the cartilages were derived 
from the ectoderm. Necturus was especially favorable in this 
respect, for its cells are larger and pigment is absent. At 
about the stage of the formation of the ganglienleisten, the 
differences between the entoderm and mesothelial tissues on 
the one hand, and the ectoderm on the other, were very great, 
the former being loaded with yolk granules, the latter contain- 
ing comparatively few. Further, the layers readily differen- 
tiated by staining with the Erlich-Biondi mixture. With the 
formation of the ganglienleisten from the ectoderm, its cells 
could be distinguished in the same way, and it was found that 
only the dorsal portion of ridge becomes nervous, the lower 
contributing its cells to the mesenchyme, while between the 
two regions there was a portion which contributed to both tis- 
sues. These ectodermal mesenchymal parts (mesectoderm, as 
Miss Platt calls them) can readily be distinguished after their 
separation from the parent layer by the peculiarities already 
mentioned. From these proliferations tissue arises which later 
forms the gill cartilages, while further in front, near the eyes 
and the nose, similar ingrowths are seen, and especially in the 
region where the mouth is to break through. From these last 
arise at least the trabecular cartilages; the origin of the para- 
chordals and otic capsule is not given. 
In a second paper (93°), Miss Platt further elaborates some 
of her earlier statements, illustrating the parts with three fig- 
ures, one of which shows the downward growth of the mesecto- 
derm, to use her extremely convenient term, between the gill 
clefts and in the region of eye and nose. 
Before the appearance of Miss Platt’s second paper, Gorono- 
witsch published his detailed account (’93), fully confirming 
