204 RITTER. (Vor. XII. 
This declaration was made in the face of a full appreciation of 
the general danger there is in unqualified affirmations that 
certain developmental processes do zot¢ take place ; but in this 
instance I believe such positiveness is justified. I must give 
my reasons for believing so with particular care and detail, 
because of the slight uncertainty of my conclusion that the 
inner vesicle is the source of the Az/age, and furthermore 
because of the supposition by Van Beneden et Julin (87) that 
the ganglion originates from the ectoderm in the C/lavelina 
bud. 
It is in the character of the ectoderm and the relation of the 
Anlage to it that my conviction finds its justification. The 
ectoderm is composed of a single layer of cuboid cells, so large, 
regularly placed, and distinctly set off from one another that 
they are quite diagrammatic in their clearness in most prepara- 
tions. The nuclei are round, and generally sharply contrasted 
with the cell-body by their distinct membrane and their less 
deeply stained ground substance. They are as a rule situated 
somewhat nearer the inner side of the cells. 
The inner surfaces of the cells are remarkably even and 
clear cut, and the layer of protoplasm forming them appears to 
be denser than the rest of the cell-body; at least, it is generally 
stained more deeply (Figs. 68, Pl. XVI, and 72 and 74, Pl. XVII). 
From this character of the individual cells the inner surface of 
the layer which they compose appears in sections as a very sharp 
line; and as this line would have to be broken were cells to 
enter the body space from the layer, either by cell division, or 
by migration, I cannot believe the process could escape all the 
search I have devoted to the point. Further than this the dis- 
tinctness of the cells from those adjacent to them in the body 
space and those composing the Az/age is evidence to the same 
end. Their nuclei are in general smaller ; but the most impor- 
tant difference is in their behavior toward reagents. By some 
methods of treatment, most markedly apparent perhaps in 
some specimens preserved in Perenyi’s fluid and stained with 
Kleinenberg’s Haematoxylin, the protoplasm of the ecto- 
derm cells, after having been decolorized, shows a dark dirty 
greenish tint that is entirely characteristic of them, not only 
