Regeneration in Compound Eyes oj Crustacea 213 



to determine just how much of the abnormal appearance of the 



tissue was due to degeneration before the death of the animal and 

 how much was due to disintegration after its death. 



It is evident that this sort of pigment development, whatever 

 may be its cause, does not belong to the normal regeneration of an 

 eve. Further, it appears probable that the causes leading to its 

 formation are of such a nature that thev inhibit the true regenera- 

 tive process. The last two cases described in the preceding 

 section furnish evidence of this. In the eves shown in Figs. 19 and 

 20 regeneration of normal ommatidia had begun but was hmited 

 bv some opposing factor. These causes not onlv inhibit the true 

 regenerative processes after thev have begun but it is also probably 

 true that thev even prevent true regeneration from beginning. 

 All the comparative evidence that we have indicates that in the 

 case of the Palaemonetes viridis previously described ( Fig. 1 7 > a 

 new eve would never have developed. The whole distal end of 

 the stump was filled with a mass of abnormal pigment deposiung 

 cells. Although this case is striking it is not exceptional. Similar 

 conditions have been found in varving degrees in other eve stumps. 

 There is sufficient similarity in all the cases of abnormal pigment 

 deposition to indicate that thev have in certain respects a common 

 cause. 



It is important to point out some of these similarities in greater 

 detail. A striking resemblance exists between the broken down 

 retinulse of an iniured eve and the pigment secreting cells. In 

 the early stages of the disintegration of the ommaudial structures 

 the nuclei of the retinulse frequently become separated from the 

 retinular processes. Each nucleus becomes surrounded bv a 

 rounded mass of cytoplasm which apparently has no connection 

 with other structures. The nuclei become polymorphic and not 

 infrequentlv appear divided. As the disintegration proceeds these 

 rounded nuclear cells usually disappear, but, as mentioned in a 

 preceding section, the broken down masses of pigment remain. 

 These rounded remains of the retinula? can be identified from a 

 few hours up to sixteen davs after the iniurA". They are always 

 seen a few hours after the injurv" although thev may not always be 

 present in eves examined in a week to two weeks after the opera- 



