50 



The 



"f 



*( ri'(tt. 



this layer has heen ruptured, nuclei are found which are supplied with a 

 well defined membrane surrounding granular contents. So far as the 

 nuclei are concerned, these pigmented hypodermal cells do not differ 

 materially from the adjacent hypodermal cells that are lacking in pig 

 ment, Fig. 5, h. 



Space. Below the lentigen is a large space, which, in the living animal, 

 is probably filled with fluid, for in none of my preparations is there any 



trace of structural ele 

 ments. A conception of 

 the form of this space may 

 be obtained by taking a 

 truncated cone of plastic 

 modeler's clay and th rust 

 ing into the truncated sur 

 face a sphere, and suppos 

 ing that there is a con 

 vexity corresponding to 

 this hemispherical de 

 pression bulging out from 

 the base of the cone. 

 This modified truncated 

 cone (the space) has its 

 base formed by the 

 slightly curving distal 

 surface of the cells of the 

 middle layer, Fig. 4, :r, and 

 the truncated surface is 

 depressed by the in- 

 w r ardly projecting hemi 

 spherical lentigen, Fig. 

 4, I. 



That this space is not 

 artificially produced by shrinkage and consequent separation of the 

 lentigen from the middle layer of cells is sufficiently evident from the 

 constancy of its presence and form, but even more certainly from the 

 fact that the deep surface of the lentigen and the outer surface of the 

 middle layer cannot be imagined to have been in contact, for if they had 

 been, such separation would have produced ragged ruptures and given 

 conditions not shown in my series of slides. 



Middle layer. Below and proximal to the space is a single layer of co 

 lumnar cells, Fig. 4, a*. Like the lentigen, this layer is thickest in the 

 middle, and diminishes very gradually and uniformly in thickness to 

 ward the margin. The contents of these cells are granular. The nuclei 

 are situated in the proximal ends of the cells, and have coarsely granular 

 contents and very faint, if any, nuclear membranes. The cells have re 

 markably well-defined cell walls. That this layer was not attached to and 

 subsequently torn away from the lentigen by the microtome knife seems 

 to be clearly shown by the fact that this middle layer has secreted on its 

 distal surface bordering the space a thick cuticular-like structure. 



t 



FIG. 5. Section of left eye of the posterior and ventral 

 .pair, transverse to axis of body. Lens crinkled and hy- 

 podermis ruptured (abbreviations as in Fig. 4). X 300. 



