192 Mary Isabelle Steele 



through the basement membrane beneath which they can be found 

 branching over the ganghon cells. Fig. 62 shows several isolated 

 retinular cells and their proximal processes which are seen extend- 

 ing through the basement membrane and reaching to the ganglion 

 cells beneath. There is no evidence that these retinular fibers are 

 directly connected with the ganglion cells; they seem merely to 

 twine around them. 



When the fibers have reached the basement membrane they 

 may pass directly through it as the two shown in the left side of 

 Fig. 62, or they may extend along the upper face of the basement 

 membrane before entering the ganglionic mass below. The 

 retinular processes frequently branch shortly before entering the 

 basement membrane or just as they emerge below it. No special 

 nerve methods were employed yet numbers of these fibers are seen 

 branching among the ganglion cells and many are readily traced 

 from the retinular nuclei to the basement membrane (Fig. 65), 

 It is only in very favorable specimens that the fibers can be traced, 

 however, through their whole length. 



b Regeneration of the Crystalline Cones 



Up to and including the stages shown in Fig. 65 and described 

 above there is no evidence of any differentiation of the crystalline 

 cones. A definite hypodermis, however, has been formed with an 

 increased number of nuclei, from which other nuclei are separating. 

 These are the cone nuclei (Fig. 63). 



The formation of the cone nuclei does not appear to take place 

 in a uniform manner. The usual method, however, is by the 

 division of the hypodermal nuclei in a plane parallel to the periph- 

 ery, the inner nuclei thus formed being the cone nuclei. But 

 since in every ommatidium there are four cone nuclei and only two 

 hypodermal nuclei, it is evident that either the hypodermal cells 

 must divide twice or the first cone nuclei must themselves divide in 

 order to make the cone nuclei just twice the number of the hypo- 

 dermal nuclei. Observations indicate that in some cases the 

 second pair of cone nuclei arise by the division of the first pair. 

 In other cases, however, it is uncertain whether they arise in this 

 manner or whether they arise from the hypodermal nuclei. It is 



