394 CHARLES H. SPURGEON. 



their development has been arrested at this stage, can be deter- 

 mined only by a study of the developing eyes. 



However I believe that the degenerated eyes of C. setosus and 

 C. pellucidus are instances of arrested development rather than 

 examples of degeneration. The reasons for this belief are that 

 the eyes as found in the adult have a cell structure which appears 

 to be comparable to the developing eyes of Crustacea. The 

 radiate arrangement of the retinal cells of the hypodermis, is 

 suggestive of the developing ommatidium. Also the eyes of 

 the young blind crayfish, C. setosus and C. pellucidus, show about 

 the same amount of degeneration as the eyes of the adult. 



