240 Mary Isabelle Steele 



and secrete corneal facets until after all of the other ommatidial 

 structures have been differentiated. Corneal facets are never 

 apparent until after more than one moult has taken place. 



14 Ommatidia do not differentiate at a uniform rate in all 

 parts of the regenerating eye. 



15 In Palaemonetes regeneration of perfect ommatidia does not 

 take place if the optic ganglion has been injured. Hermit crabs 

 may regenerate a perfect eye after removal of as much as half the 

 optic ganglion. Crangon regenerates an eye very slowly, even 

 when the optic ganglion is uninjured, but there are evidences that 

 ommatidia may differentiate after a part of the optic ganglion has 

 been removed. 



16 The rate of regeneration is quite variable in all the species 

 experimented upon, but both hermit crabs and Palaemonetes 

 however may regenerate ommatidia within thirty-five to forty-five 

 days. 



17 Splitting the eye of Palaemonetes is not followed by regen- 

 eration if the split.extends into the optic ganglion. 



18 In the breaking down of the injured ommatidia the pigment 

 secreting cells become widely scattered, and the old pigment 

 persists for a long time. Frequent cases of abnormal development 

 of pigment also occur. There are evidences which indicate that 

 this abnormality is due to the pathological development of the 

 broken down retinulae. 



19 After removal of all or nearly all of the optic ganglion, 

 hermit crabs may regenerate a heteromorphic appendage in place 

 of the excised eye. There is, however, apparently a level from 

 which neither an eye nor an antenna-like appendage will regen- 

 erate. 



20 The nerve-trunk of the heteromorphic appendage forms a 

 continuous structure with the stump of the optic nerve. 



21 Removal of the entire eye of Crangon may also be followed 

 by the regeneration of an antenna-like appendage. 



22 In no case was there evidence that Palaemonetes vulgaris 

 possessed the ability to regenerate a heteromorphic appendage 

 after the removal of the entire eye. 



23 The results of this entire series of experiments points to the 



