Regeneration in Compound Eyes of Crustacea 193 



probable, however, that they are formed by the division of the first 

 pair of cone nuclei as can be determined in some cases. 



In the early stages of cone formation the inner surfaces of the 

 hypodermal cells lose their distinctive outlines. For" at this time 

 there is no clear line of demarcation between the hypodermal and 

 cone cells. Fig. 63 represents one of the earliest recognizable 

 stages in crystalline cone formation. The hypodermal cells are 

 more or less definitely grouped into pairs and it is readily seen that 

 cone and hypodermal nuclei are not wholly separate. Extending 

 inward from the cone nuclei are very delicate strands of cyto- 

 plasm. These strands seem to group the hypodermal nuclei into 

 pairs and by their branching and crossing form a much vacuolated 

 network. 



At a stage slightly more advanced (Fig. 64) the cytoplasm of the 

 cones has begun to assume a more definite cone shape. There is 

 still, however, no distinct line of separation between the hypo- 

 dermal and cone nuclei. Neither does the cone mass show the 

 boundarie-s of its component cells. In stages a little later the cone 

 cells begin to show individual outlines and the cytoplasm appears 

 more condensed. Cone formation is practically complete, how- 

 ever, before the corneal hypodermal and cone cells show a distinct 

 line of separation (Fig. 66). 



As the cone cells differentiate the cytoplasm becomes less and 

 less vacuolate and gradually assumes a dense granular appear- 

 ance. The cytoplasm is most condensed just below the nuclei and 

 decreases in density proximally. 



In longitudinal sections of the cones the cell boundaries appear 

 distinct from their outer ends inward to the outer retinulae. At 

 this point the cell boundaries become indistinct and the cone 

 tapers rather suddenly into a slender stalk which extends to the 

 distal end of the rhabdom, where it ends abruptly (Fig. 66). 

 At a somewhat more advanced stage the boundaries between the 

 cone and corneal hypodermal cells become distinct, and the cone 

 secretion takes on the dense homogeneous deeply staining appear- 

 ance characteristic of that in mature cones (Fig. 67). 



