42 JOHNS HOPKINS UNIVERSITY MORPHOLOGICAL MONOGRAPHS. 
on the proximal complex eye and the lateral simple eyes.* It is on 
the histological structure of some of the various parts that differences 
exist. 
Cornea.—Little need be said on the cornea except that it consists 
of flattened cells applied to the outer surface of the lens. It is 
continuous with the epithelium of the club and evidently a modified 
portion of this epithelium (Fig. 7). All observers conform to this 
statement. 
The Lens.—The lens is of cellular origin, but in its interior the 
cells are often so changed—absence of nuclei, cell walls, and pro- 
toplasmic structure—as to make a mass quite homogeneous and 
structureless. While this internal mass sometimes shows practically 
no structure, yet at other times it is found broken up into masses 
much the size and shape of cells but without nuclei, while again, 
cells with nuclei may be quite evident. This occasional breaking 
up of this mass is evidently predetermined by its original cell 
structure. Iron-hematoxylin stains this inner mass very dark and 
it is difficult to wash out the stain. Borax carmine and Lyons 
blue give the best results on the lenses. In figure 7 the lens of 
the distal complex eye is shown as quite homogeneous internally, 
while in figure 13 (proximal complex eye) it is drawn cellular. In 
this latter lens the inner cells are quite round and nucleated as 
they may also appear in the distal eye. What I have said applies 
equally to the lenses of both complex eyes, though the cellular 
nature of the inside of the lens is more readily demonstrated in 
the proximal eye. 
It appears that it is in younger specimens that the central mass 
of the lens shows the cellular structure best, and that as the animal 
grows older this structure is more and more lost until no trace 
* Haake? says that in the adult Charybdea Rostonii the vitreous bodies of 
the complex eyes are absent but present in the young. It is difficult to 
explain this observation except on grounds of imperfect preservation of the 
adult material, for in all observations on other forms a vitreous body is 
described. Haake evidently did not use sections, and for this reason his 
results must be regarded as of doubtful accuracy. Haake also says that the 
simple lateral eyes of the clubs are absent in the adult, but present in the 
young. 
