ESTERLY: EUCALANUS. 21 
bodies, considered in their spatial relations, are not really plate- or 
dise-like. It seems to me that this is possibly the case, though I 
have been unable to satisfy myself completely of the correctness of this 
view by following them on serial sections. And I can not see that in 
entire preparations of the eye the interior bodies have the form of 
plates. On the contrary, they always appear to be rod- or spindle- 
shaped. If the bodies are not discs or plates, it seems that the other 
alternative which will account for their positions in the cell is to con- 
sider that some of the rod-like forms are parallel to one axis of the 
cell, and some to another axis. For example, in comparing the central 
cells in Figures 5 and 7 (Plate 1), the one seen in frontal, the other in 
cross section, it is plain that in each case there are interior bodies 
which are arranged with reference to the longer of the two axes of the 
cell which appear in each of the two figures. 
Structures which seem to be of a nature similar to the interior bodies 
of Eucalanus, have been described for other Copepoda and lower 
Crustacea. Hartog (’88, p. 34) states that there is an “‘oblong body 
(probably a rhabdome) staining deeply with osmic acid,” “‘in the 
inner limb of each bacillus,’ and Claus (91) has mentioned the 
general occurrence of “Cuticular-stabchen” in many other crustacea 
possessing a median eye, as well as in Diaptomus, Anomalocera, 
Pontellina and others among the Copepoda. One can not fail to note 
a certain similarity between the condition he figures in the dorsal eyes 
of Pontellina mediterranea (Claus, ’91, Taf. iv, Fig. 6-8) and those in 
Eucalanus. He states (p. 350) that the cuticular rods were intensely 
colored in borax carmine or haematoxylin, and were not straight, but 
curved, and joined in pairs at their thickened ends. Parker (91, 
p- 81) says that in the portion of the retina surrounding the cone in 
Pontella “‘the most conspicuous structures ....are rod-like bodies, 
which probably represent rhabdomeres.” He detected eight such 
bodies, and believes that there is a cell for each rod, because a large 
nucleus is near each of the latter. Consequently it would seem, that, 
if the rhabdomeres and ‘“Cuticular-stibchen” are homologous with 
the interior bodies, the numbers do not nearly correspond in the vari- 
ous cases where the structures occur. ‘There is certainly more than 
one interior body for each nucleus in the retina of Eucalanus. Hesse 
(:01, p. 351) mentions the similarity of the structure in the retinal cells 
of Eucalanus with the interior bodies in the visual cells of the leeches 
and in the problematical visual cells of the Lumbricidae. 
f. Relation of Axis Cylinders to Retinal Cells—— That the interior 
bodies in the cells of the eye of Eucalanus have a functional importance, 
