Regeneration in Compound Eyes of Crustacea 217 



cuticle by the multiplication of the cells beneath. In these cases 

 a true hypodermis is not distinguishable. These facts suggest that 

 the migration and pathological development of the old retinulae 

 are responsible for most if not all of the cases of abnormal pigment 

 deposition. This of course does not explain what induces this 

 pathological development. 



The initial cause of this development, in the cases v^here an 

 abundant network of tissue has developed, was perhaps due to 

 some infection at the time of the operation. This is suggested by 

 the fact that, in the crayfish eye described above, a great deal more 

 tissue had developed abnormally in sixty-two hours than is usually 

 developed normally in ten days or two weeks, and by the fact, also, 

 that in the eye of Palaemonetes viridis a very unusual amount of 

 new tissue had developed during the first nine days after the injury. 

 The more frequent cases in which the pigment secreting cells 

 appear as rounded cells, containing polymorphic nuclei similar to 

 the disintegrating retinular cells, seem to be produced by causes 

 somewhat different. In some specimens examined some time 

 after the injury these cells show no signs of rapid multiplication. 

 It seems probable that these cells are old retinulae that have 

 retained one of their characteristic functions, the secretion of 

 pigment. Since it is an observed fact that the old retinulae become 

 metamorphosed and wander to different parts of the stump where 

 they have been found dividing amitotically. 



While the above facts are strongly in favor of the conclusion that 

 the abnormal pigment-secreting tissue is due to the development 

 of old retinular cells yet the proof is not absolute. A series of 

 stages of this development, not more than two days apart, would 

 have to be examined in order to be certain of the absolute truth 

 of this tentative conclusion. 



2 Eye Stumps that Show iVo Regeneration 



It now remains to consider the other phase of the subject out- 

 lined in this section; namely, those cases in which there is no 

 regeneration further than the healing of the stump. A number of 

 these cases present anomalies in that there is no apparent reason 



