MUSEUM OF COMPARATIVE ZOOLOGY. 107 
The rhabdome (Figs. 94 and 95, rhb.) in Gonodactylus is an elongated 
rod-like structure of uniform thickness, which extends from the region 
of the proximal retinular nuclei to the basement membrane. It shows 
a distinctly toothed edge (Fig. 94), especially in specimens which have 
been treated with potassic hydrate. In transverse section it is squarish. 
Owing to its small size, the exact relation of the seven surrounding cells 
to its four faces cannot be easily determined. The single unpaired cell 
(Fig. 101) certainly lies opposite a face, not an angle. In this respect 
it agrees with the unpaired cell in Squilla as figured by Grenacher (’79, 
Taf. XI. Fig. 122). Probably in Gonodactylus the remaining six cells 
are related to the sides of the rhabdome as the corresponding ones are 
in Squilla (compare Grenacher’s Fig. 122). In Gonodactylus the retinu- 
lar cells and rhabdome are in close. contact with one another. The 
separation of these elements as figured by Grenacher in Squilla is prob- 
ably artificial, as Grenacher himself suggests. In Squilla, according to 
both Steinlin (’68, p. 17) and Grenacher (’79, p. 125), the rhabdome 
in transverse sections is subdivided into four equal parts, somewhat as 
in Mysis. I have not observed this condition in Gonodactylus. 
The distal retinular cells in Gonodactylus occupy the usual position 
near the cones. They contain very little pigment, and their number 
can be determined only by that of their nuclei. These agree with the 
nuclei of the proximal cells in the possession of a single well defined 
nucleolus, which is most readily seen in depigmented sections (compare 
nl. dst. and nl. px. in Fig. 94). The distal nuclei, especially in the 
region of the larger ommatidia, are arranged in rows which alternate 
with the rows of cones (Fig. 99, n/. dst.). Although the nuclei are not 
very definitely arranged, they often show a tendency to be grouped in 
pairs, and these pairs are so placed that in each row there is evidently 
one for each adjacent ommatidium. Moreover, in equal lengths of ad- 
joining rows of nuclei and cones, the nuclei are always double the num- 
ber of cones. _I am convinced by these facts that there are two distal 
retinular cells for each ommatidium. 
Besides the cells already deséribed, certain others occur in the proxi- 
mal part of the retina in Gonodactylus. These are represented by a 
few small, elongated nuclei (Fig. 94, nd. ms’drm.), which are very similar 
in appearance to certain nuclei occurring in the spaces below the base- 
ment membrane. I therefore believe that in Gonodactylus, as in Mysis, 
the proximal portion of the retina is occupied by intrusive cells, which 
are probably mesodermic in origin. 
The kinds of cells found in the ommatidium of Stomatopods are as 
