194 Mary Isabelle Steele 



c Regeneration of the Rhabdoms 



There is no indication that the retinular cells have begun to 

 secrete the rhabdoms until after the cones have been distinctly 

 outlined, although the retinulae themselves become clearly differen- 

 tiated before there is any indication of the cones. Not until the 

 differentiation of the ommatidia has reached a stage intermediate 

 between these stages shown in Figs. 64 and 66 can the anlagen of 

 the rhabdoms be recognized. The rhabdoms first appear as 

 slender homogeneous rods. Each rod is of uniform diameter 

 throughout its length, and is distinguishable from the inner ends of 

 the cone cells only by the fact that it stains slightly deeper and 

 shows no divisions which indicate that it is composed of more than 

 one cell (Fig. 66.) The rhabdoms show no signs of the character- 

 istic spindle-like form and the complicated system of transverse 

 plates so noticeable in the normal adult eye until after the last 

 stage in the differentiation of the cones (Fig. 67). Even at the 

 stage shown in the preceding figure the rhabdom does not show a 

 normal appearance of its spindle form and the pigmented exten- 

 sions of the retinular do not cover it so completely as in normal 

 adult ommatidia. 



It is evident from the preceding description and accompanying 

 figures that all the structures necessary to a completely regenerated 

 eye have been laid down. It is also seen that with the exception 

 of the corneal facets the regenerated ommatidia are practically 

 identical with those of the normal adult eye. A specimen of later 

 stage, however, shows both the corneal facets and the definitive 

 form of the rhabdom, so that the regenerated ommatidia present a 

 perfectly normal appearance even to the minutest detail (Fig. 76). 



All observations show that the differentiation of corneal facets 

 could not become evident until after at least two moults. The 

 first cuticle which is developed is formed before a continuous 

 hypodermis has grown over the wounded surface and before any 

 regeneration of ommatidia has begun. Corneal hypodermal cells 

 are not differentiated as such until all of the other ommatidial 

 structures have been laid down. Therefore the secretion of 

 corneal facets constitutes the final process in the regeneration of 



