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-haematoxylin 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 2 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. 



