Regeneration in Compound Eyes of Crustacea 199 



differentiation in the embryonic eye of the lobster as described by 

 Parker (/oc. cit.) Further, these observations upon regenerating 

 eyes agree with those of Philhps upon the developing compound 

 eye of the honey bee in regard to the order of appearance of the 

 retinulae and cones, in the method of innervation of the ommatidia 

 and in regard to the relation of the cones and rhabdoms. In the 

 developing eye of the honey bee, however, Phillips finds the rhab- 

 doms partially differentiated before there is any indication of the 

 cones. On the other hand in the regenerating eyes of hermit 

 crabs and Palsemonetes the cones are definitely formed before any 

 rhabdoms can be recognized. The variations, however, which 

 have been noted between the developing compound eye of the 

 honey bee and the regenerating eyes of Palaemonetes and hermit 

 crabs, cannot be regarded as fundamental. Such differences are 

 perhaps not more marked than those that would be noted if the 

 embryonic development of the same eyes were compared. 



It is scarcely necessary to add that these observations on regen- 

 erating eyes are in several respects quite at variance with the 

 observations of Kingsley and Patten, who find the rhabdoms 

 developed from an inward prolongation of the cone cells, the cones 

 formed as extracellular secretions and the ommatidia innervated 

 by nerve processes coming from the optic ganglion and penetrating 

 the rhabdoms and cones. 



/f. Differences in the Regeneration of the Eye Among PalcB- 

 monetes, Crangon and Hermit Crabs 



Reference has already been made to the fact that certain differ- 

 ences in the regenerating eye appear among Palaemonetes, Crangon 

 and hermit crabs. The rate of regeneration and the ability to 

 regenerate varies greatly in these different genera although in the 

 most essential particulars the regeneration of the ommatidia is 

 similar. It has been seen that hermit crabs may regenerate an 

 eye after the removal of half the optic ganglion. But neither 

 Palaemonetes nor Crangon regenerate a perfect eye if the injury 

 includes any part of the optic ganglion. It has also been seen that 

 the differentiation of the ommatidia takes place more rapidly in 



