134 PATTEN. [Vot. II. 
general character of the invagination points to this conclusion, 
and it seems hardly possible to reconcile, by an explanation 
along any other line, the independent development of such de- 
pendent structures as the eye and the optic ganglion. 
The sections shown in Figs. 24-27 belong to a little younger 
stage than those shown in Figs. 20-23. They were cut from an 
embryo somewhat abnormal, the antenne being lodged in a 
great depression, on the floor of which was the mouth. There 
was nothing abnormal about the parts belonging to the eyes. 
The first and second ganglionic invaginations are shown particu- 
larly well. 
All these sections and those described above are instructive 
from the fact that there cannot be a shade of doubt that the 
ganglionic invaginations have nothing whatever to do with the 
formation of optic vesicles, for the peculiar way in which the 
eyes develop makes it possible to determine, even at this period, 
just what parts develop into the eyes and what into the optic 
ganglion. 
These two series of sections show pretty clearly that chere 
are two distinct, and onze obscure, invaginations to form the optic 
ganglion. This fact ts of especial interest when we consider that 
there are three segments to the brain and three to the optic plate, 
and three distinct parts to the optic ganglion of the convex eye. 
In Fig. 3 a the three ganglionic segments, o. ¢.¥? are still visi- 
ble in surface views, and at the anterior ends of the first two are 
seen the openings of the ganglionic invaginations, g. v.t and g. v.2 
In a later stage (Fig. 4), nearly all the eyes, as well as the 
mouths of the two invaginations, are visible. Still later (Figs. 
5 a and 6) the invaginations have disappeared, and all but a small 
part of the optic ganglion is concealed by the optic plate. 
Just after the rupture of the embryonic membranes, the optic 
ganglion is completely shut off from the surface, and the ecto- 
derm of the optic plate becomes continuous with that over the 
brain. é 
Figs. 28-34, Pl. IX., represent seven sections of an embryo 
about the age of that in Fig. 4. 
The optic ganglion now forms a great, complex mass of cells, | 
the most of which is not yet overgrown by the optic plate. It 
requires careful attention, not only to recognize its parts, but to 
distinguish them from the brain. 
