108 BULLETIN OF THE 
follows : cells of the corneal hypodermis, two ; cone cells, four ; proxi- 
mal retinular cells, eight, one of which is rudimentary ; distal retinular 
cells, two ; accessory cells (mesodermic?) present. 
Decapoda. 
I have studied the eyes of the following species of Decapods: Gelasi- 
mus pugilator, Latr.; Cardisoma Guanhumi, Latr.; Cancer irroratus, 
Say ; Hippa talpoida, Say ; Palinurus Argus, Latr. ; Pagurus longicarpus, 
Say ; Homarus americanus, Edw.; Cambarus Bartonii, Fabr ; Crangon 
vulgaris, Fabr.; and Palemonetes vulgaris, Say. I collected much of 
this material at the Station of the United States Fish Commission at 
Wood’s Holl, Mass. The specimens of Cambarus were obtained in the 
vicinity of Philadelphia. I am under obligations to Mr. Herbert M. 
Richards for specimens of Palemonetes collected by him at Newport, 
R. I. A number of eyes of two Crustaceans, Cardisoma and Palinurus, 
were kindly obtained for me by Mr. Isaac Holden; they were collected 
on the coast of Florida by Mr. Ralph Munroe, to whom I am indebted 
for the careful way in which they were preserved. 
The corneal hypodermis in Decapods was first recognized by Patten 
(86, pp. 626 and 642), who observed it in Penzeus, Palemon, Pagurus, 
and Galathea. Since Patten’s announcement of the presence of this 
layer in Decapods, it has been identified in a number of other genera: 
in Crangon by Kingsley (86, p. 863), in Alpheus by Herrick (’86, p. 43), 
in Astacus by Carriére (’89, p. 225), in Cambarus and Callinectes by 
Watase (90, pp. 297 and 299), and in Homarus by myself (’90%, p. 6). 
More recently I have observed it also in Paleemonetes (Plate IX. Fig. 
103, cl. crn.), Crangon, Cambarus, Palinurus, Pagurus, Hippa, Cancer, 
and Cardisoma. 
In almost all Decapods in which the arrangement of the cells in the 
corneal hypodermis has been observed, these elements have been found 
to be grouped in pairs, and so distributed that each pair occupies the 
distal end of an ommatidium (compare Figs. 103 and 106, Plate IX.), 
This arrangement has been observed, either by others or by myself, in 
the genera mentioned in the preceding paragraph, except Callinectes, 
in which the exact arrangement of the cells has not been recorded, 
Reichenbach’s statement (’86, p. 91), that in Astacus there are four 
hypodermal cells under each facet, is probably erroneous, as Carriére’s 
observations show, 
Although Patten was the first investigator who clearly demonstrated 
the presence of the corneal hypodermis in Decapods, Grenacher, in 1879, 
