54 BULLETIN OF THE 
-the retina the intercepting membrane had the appearance of a delicate 
lamella, in which I was unable to find any trace of cells. Not unfre- 
quently the nuclei of certain accessory pigment cells (Fig. 2, nl. ’drm.) 
appear to touch the membrane, and even at times to lie with their long 
axes parallel to it, but in no case could these nuclei be said to be zm the 
membrane. In sections of the retina from which the natural pigment 
had not been removed, it was often diffivult to decide whether a given 
nucleus was 7z the membrane or only neat to it. Possibly appearances 
such as these have led Carriere to believe that the membrane was cel- 
lular. My own opinion is, that the intercepting membrane, like the 
other two membranes, is a cuticula, and does not contain cells. 
From the foregoing account, it will be seen that in an adult Gammarus 
the retina lies immediately under an undifferentiated corneal hypoder- 
mis, and is enclosed, excepting where the optic nerve emerges from it, 
by a non-perforated cuticular capsule. The space within this capsule 
is divided by a perforated cuticular membrane into a large distal and a 
small proximal chamber, 
In Hyperia, judging from the figure given by Carriere (’85, p. 161, 
Fig. 123), the retina has essentially the same structure as in Gammarus. 
The intercepting membrane is in a position proximal to the rhabdomes 
and distal to the retinular nuclei. The layer of pigment cells, which 
Carritre (’85, p. 161, Fig. 124) apparently considers the intercellular 
membrane itself, in my opinion marks only approximately the position 
of that membrane. Probably in Hyperia, as in Gammarus, these cells 
rest on the distal face of the intercepting membrane. 
In Phronima each side of the head is occupied by two eyes, instead of 
one, contrary to the condition in the more typical Amphipods. Of the 
two eyes, one is dorsal, the other lateral. This difference in position 
affords a convenient means of distinguishing them. The lateral eye pre- 
sents all the essential structural features of the single eye in Gammarus 
(compare Carriére, ’85, Figs. 125 and 121). The dorsal eye, although 
differing considerably in shape from the lateral one, is nevertheless con- 
structed upon the same morphological plan. Its most important pecu- 
liarity is the shape of its intercepting membrane and the adjoining 
structures. In the dorsal eye the intercepting membrane, instead of 
lying in a plane nearly parallel with the external surface of the retina, 
as in the lateral eye, is cone-shaped. The axis of this cone corresponds 
to the axis of the eye; its apex is near the brain, and its base faces the 
external surface of the eye (compare Claus, ’79, Taf. III. Fig. 20, and 
Taf. VII. Fig. 58). The ommatidia are arranged approximately parallel 
