esterly: eucalanus. 21 



bodies, considered in their spatial relations, are not really plate- or 

 disc-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. Consec[uently it would seem, that, 

 if the rhabdomeres and "Cuticular-stabchen" 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, 



