Regeneration in Compound Eyes of Crustacea 201 



continuous hypodermis has not yet been formed. A considerable 

 area between the cuticle and the outer retinulae is occupied by a 

 granular structureless mass. Just to one side of this area is a 

 region in which none of the old ommatidia appear but in which 

 there are new ommatidia almost completely formed. No more 

 than five of these appear in any one section. These lie near the 

 basement membrane toward the inner edge of the eye. Con- 

 sequently these new ommatidia lie next the growing zone, always 

 present in the eyes of young individuals as described in Section III- 

 It is apparent then in this particular case that it is impossible to 

 determine conclusively whether the new ommatidia are regenerated 

 or normally developed ommatidia. In other cases, however, new 

 ommatidia are found developing in positions where it is evident 

 they are regenerating ones. 



From the evidence obtained by an examination of a number of 

 regenerating eyes of Crangon it seems that the rate of regeneration 

 depends largely upon the rate of removal of the injured tissue. 

 The failure of the old tissue to degenerate prevents the regeneration 

 of new structures. Since the injured ommatidia, although they 

 fail to break down for a considerable time at least, are incapable 

 of regeneration in themselves. We should perhaps expect the 

 cones to be incapable of any sort of regeneration for the cone 

 nuclei have been destroyed and the constructive metabolic activity 

 of a cell apparently depends largely upon the nucleus. The nuclei 

 of the retinulae, however, have not been injured and still retain 

 much of their normal appearance. But there is no evidence that 

 the retinulae ever take part in normal regeneration. 



A comparative study of the regenerating eyes of Palaemonetes 

 and Crangon shows that the difference in the rate of regeneration 

 is in reality largely a difference in the rate of degeneration of the 

 injured tissues. In Palaemonetes the injured tissues usually 

 break down rapidly and are quickly removed. In Crangon they 

 persist indefinitely. Hence regeneration in Palaemonetes begins 

 soon after the injury, and new ommatidia may be almost fully 

 developed in shorter time than is required by Crangon for the 

 removal of the injured ommatidia. The specific case of Crangon 

 perhaps suggests that if all of the ommatidia had been completely 



