76 Frederick H. Krecker, 



sligthly ectad of the center at the point where the optic nerve enters. 

 Enclosing the whole is a thin, almost imperceptible enveloping mem- 

 brane. Beginning with the lens each of these parts will be described 

 more or less in detail. 



The lens is a circular, transparent body and is extremely large; 

 its size being almost equal to that of the remainder of the eye. It 

 is of a homogeneous composition, except for a thin, yellow layer over 

 its outer surface which somewhat resembles the ordinary chitin and 

 is probably slightly hardened to act as a protection. In the body of 

 the lens are sometimes seen a series of concentric circular striations. 

 The lens' distal periphery has a greater radius than the proximal with 

 the result that a pointed, hornlike projection overlaps the distal end 

 of the underlying cells (Fig. 9 and 10). On the exterior, where the 

 lens meets the body, it is encircled by comparatively deep groove 

 chiefly due to a pushing out of the body wall into a ridge. 



Between the lens and the visual rods is the extremely flattened 

 layer of corneal hypodermis which at times, depending upon the age 

 of the adult individual, is barely visible. This condition is due to the 

 fact that the lens is formed at the expense of the corneal hypodermis 

 which fact is likewise the cause of the disintegrating appearance of 

 the layer. It will be considered again in connection with the description 

 of the development. The cells of the corneal hypodermis are indistinct 

 in outline, being frequently indicated only by the presence of somewhat 

 compressed and elongated nuclei. Of these five at the most have 

 been noticed, generally three or four and often in the adult but two. 

 The peripheral cells are somewhat the longer, extending further both 

 distad and proximad than the others, thus in the latter direction over- 

 lapping the visual rods (Fig. 9 and 10). 



Surrounding the corneal hypodermis is a single row of large cells 

 which deserve special attention. In a longisection of the eye they 

 may be seen between the corneal hypodermis and the adjoining body 

 wall, their broad bases lying below the visual rods, almost on a level 

 with those of the retinal cells. The body of the cell tapers distad beyond 

 the corneal hypodermis (Fig. 10). There is a large, circular, basally 

 situated nucleus with a well defined nuclear network on which are 

 scattered large particles of chromatin. The cells are densely covered 

 with pigment and from their position may be considered to act as a 

 sort of iris which prevents lateral T&ys of light from striking the visual 

 rods (Fig. 9). The iris cells described by Hesse, Redikorzew and 

 others as existing in the forms studied by them, are not so highly 



