182 RITTER. iV Or ei 
than are those reached by some later students under conditions 
reversed as to technique and intellectual freedom. 
Among the earlier works to which reference is above made 
those of Giard (72), and Kowalevsky (74a and '74b), are 
particularly to be mentioned. 
The results of my study of both Goodsirza and Perophora 
agree essentially with this last view; but since in neither 
genus were they reached without special perplexities, I must 
present the facts with considerable detail. In Goodsiria the 
formation of the ganglion is by no means a complicated process, 
but the difficulty in finding just how it occurs is due to the 
apparent quickness with which it becomes fully separated from 
its source, which is, I may say in a word, the ventral wall of 
the hypophyseal duct. At the time of writing my preliminary 
paper I was still in some doubt about its source, but more 
careful study since leaves, as I hope the following will show to 
the satisfaction of every reader, no room for question. Fig. 40, 
Pl. XVI, presents a transverse section of the duct in the earliest 
stage that I have found after its complete separation from the 
primitive inner vesicle. That the stage is one very soon after the 
separation takes place is certain from the state of development 
of the other organs of the bud as compared with the stage in 
which the duct is still merely a groove-like evagination. The 
peribranchial sacs are very slightly developed, the dorsal parti- 
tioning fold of the right side being barely indicated in this posi- 
tion, while the left does not appear at all in the section. Yet 
it is seen that the ganglion, ¢/., though very small, is already 
distinctly separated both from the wall of the primitive vesicle 
beneath it, and from the duct above it. The condition here 
shown, and even a slightly earlier one, but with the separation 
still complete, occurs not infrequently ; but the critical stage, 
the one between this and that with the duct in the groove con- 
dition, escaped me for a long time, and made it seem quite prob- 
able that the cells entering into the ganglion were derived from 
some other source than the duct or primitive vesicle, z.e. either 
from the ectoderm or from the surrounding mesenchyme cells. 
In only three or four buds have I found the decisive stages, 
but two of these, those from which Figs. 44-47, Pl. XV, 

