Regeneration m Compound Eyes of Crustacea 195 



ommatidia. Since this is true, several moults may occur before 

 the corneal facets differentiate, and at least two must take place. 



J Comparison of Ommatidia in Regeneration and Ontogeny 



In comparing the regenerating with the embryonic eye it is 

 necessary to consider them only from the beginning of ommatidial 

 differentiation, since there can be no exact parallel between the 

 preliminary stages of regeneration and the mode of the origin of 

 the embryonic eye. These two processes are similar, however, in 

 the respect that the ommatidia in both cases develop from the 

 hypodermal cells. All these observations upon the regenerating 

 eye give evidence that the cells which take part in the formation 

 of the new ommatidia are derived primarily from the hypodermal 

 cells that cover the wounded surface. That the ommatidia of the 

 embryonic eye develop entirely from the hypodermis is the con- 

 clusion of most observers. There is no further agreement, how- 

 ever, in details except in the case of embryonic eyes that are 

 described as arising without invagination, <?. g., the compound 

 eye of the honey bee as described by Phillips ('05) and of the 

 lobster (Parker '90), in which it was found that the ommatidia are 

 developed from a single epithelial layer and consequently from 

 morphologically similar cells. 



It has been seen that the first cells differentiated from the hypo- 

 dermis in the regenerating eye are the retinular cells. This can be 

 regarded as being in agreement with the conclusion of Phillips 

 that the retinulae constitute the morphological center of the 

 ommatidium. At any rate the retinulae are in each case differen- 

 tiated before the cone cells can be recognized, none of the cells 

 originally separated from the hypodermis to form the retinulae 

 ever take any part in the formation of cones, and finally the cone 

 cells arise peripheral to the retinulae. 



The differentiation of the regenerating ommatidia, described in 

 a preceding section, and of the embryonic eye, as described by 

 Kingsley ('87), may perhaps be regarded as presenting a parallel. 

 Kingsley finds the nuclei which go to make up the cones and re- 

 tinulae arranged in radial rows and that the outer and hence the 



