The Internal Anatomy of Spiders 



pg.sl.~- 



The nerve fibres enter the retina through the cross slits as well 

 as through the long one. Figure 170 is a diagram representing 

 one end of a grate-form tapetum, the figure is a composite one, 

 the upper half representing the tapetum, as observed by Shafer, 

 of Lycosa helluo, and the lower half, that of Pardosa lapidicina. 



In this figure, /. si. represents the longitudinal slit and c. 

 si., the cross slits; both of these are filled with pigment excepting 

 the spaces occupied by the nerve fibres, sections of which are 

 represented as white spots. The white spaces, t., alternating with 

 the cross slits, represent the tapetum strips. Extending in from 

 the rim of the cup, which is 

 heavily pigmented, there is a 

 strip of pigment, pg. 3/., upon 

 each tapetum strip. In each 

 half of the figure, the rod end, r., 

 of several visual cells is repre- 

 sented. These cells are sur- 

 rounded by pigment except where 

 they rest upon the tapetum. 



The pigment cells. — Cells con- 

 taining a dark pigment occur in 

 various situations in and about 

 the eyes of spiders. These pig- 

 ment cells, limiting as they do the 

 transparent tracts that may be 

 followed by the light, doubtless 

 play an important part in the 

 operation of the eye. 



A ring of hypodermal cells 

 about the rim of the eye and 



immediately under the edge of the lens that contains pigment is 

 termed the iris (Fig. 169, i). The iris pigment occurs both in 

 the undifferentiated hypodermis and in the marginal cells of the 

 corneal hypodermis. 



In eyes of the postbacillar type (the anterior median eyes) 

 there are interstitial pigment cells between the visual cells 

 (Fig. 167,). In some species the pigment cells extend to the 

 corneal hypodermis; in others they reach only the proximal end 

 of the optic rods. 



In eyes of the prebacillar tvpe (all eyes except the anterior 



[65 



Fig. 170. DIAGRAM OF 0\ T E END 



OF A GRATE-FORM TAPETUM 



(after Shafer) 



