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MUSEUM OF COMPARATIVE ZOOLOGY. 105 
be recognized easily. Directly under the corneal cuticula each pair of 
hypodermal cells is in contact with similar pairs belonging to adjoining 
ommatidia, so that the layer here forms a continuous sheet. In a more 
proximal plane the neighboring pairs of hypodermal cells are not in con- 
tact (compare Fig. 93, a tangential section in which the extreme right- 
hand edge represents the condition immediately below the cuticula, while 
the parts to the left represent central portions successively more proxi- 
mal in position). The only indication of a separation between the two hy- 
podermal cells of each pair is seen in the distal projection of the cone 
between the two hypodermal nuclei-(compare Figs. 94 and 96, con.). 
The corneal cuticula in Gonodactylus is facetted, but the proximal and 
distal faces of the facets are apparently plane. Over the smaller om- 
matidia the facets are hexagonal in outline, whereas over the larger ones 
they are rectangular, and their arrangement is often indicative of the 
tetragonal system. In Squilla mantis, according to Will (’40, p. 7), the 
facets are hexagonal. 
The cones in Gonodactylus are composed for the most part of a uni- 
formly granular substance. Distally, they are pointed and probably 
touch the corneal cuticula; proximally, they terminate at the rounded 
end of the rhabdome (Fig. 94). Each cone contains in its distal enlarge- 
ment four nuclei (Fig. 97, nd. con.), two of which lie directly proximal 
to the nuclei of the corneal hypodermis, while the remaining two alter- 
nate with them (compare Figs. 96 and 97). The proximal part of the 
cone is divided longitudinally into four segments (Fig. 98). Each seg- 
ment, if extended distally, would include one of the four nuclei, and 
corresponds to one of the four cells by which the cone was produced. 
In Squilla mantis, according to Steinlin (’68, p. 17), the cone is also 
composed of four segments. 
The retenular cells of Gonodactylus are of two kinds, proximal and 
distal. The proximal cells, constituting the retinula itself, surround the 
rhabdome completely, and extend distally only a short distance beyond 
it (Fig. 95). They contain only a small amount of pigment, which is 
concentrated in two regions, at their distal ends and near the basement 
membrane. The rhabdome is surrounded throughout its length by a 
thin but rather dense layer of pigment. This layer is more extensive 
in the smaller ommatidia (Fig. 102) than in the larger ones. The 
nuclei of the proximal retinular cells (Figs. 94 and 95, nl. px.) are 
located near their distal ends. 
The number of cells in the retinula of Squilla, as described by Grena- 
cher (77, p. 33) and by Hickson (’85, p. 341, Fig. 2), is seven. In 
