210 Mary Isahelle Steele 



remains of the old ommatidia although they are greatly sea;: red 

 through the new tissue. A few dense cysts of new pig ,ent, 

 however, have been formed and other pigment secreting ct irers 

 have begun to appear. From these observations it seems ap] • irent 

 that had the animal lived the entire mass of tissue sooner or iarer 

 would have been densely packed with pigment cysts and that very 

 probably new eye structures would not have regenerated. F< r we 

 have seen in the preceding two cases that an abnormal secreii .m of 

 pigment stopped, apparently, ommatidial regeneration a- r it 

 had begun. It does not seem too much to assume then that in 

 this case normal regeneration of tissues would have been precluded 

 by such an abundant development of abnormal tissue. 



C EYE STUMPS THAT SHOW AN ABNORMAL DEVELOPMENT OR NO 



REGENERATION 



The instances described in the preceding section apply partic- 

 ularly to those unusual types in which the ommatidia have begun 

 to regenerate and this process has been more than balanced by 

 opposing factors. This leads naturally to a consideration of cases 

 in which there is either no regeneration or only an abnormal 

 development of pigment. 



I Abnormal Development of Pigment 



Most of the examples of abnormal pigment secretion were 

 afforded by Palaemonetes in which the optic ganglion was more or 

 less injured. Usually in any of the forms studied eye stumps that 

 contain no more than half of the optic ganglion show no normal 

 regeneration aside from the cuticle and hypodermis. Any attempt 

 to regenerate other tissues produces either scattered strands of 

 connective tissue or abnormal masses of pigment. These pigment 

 masses most frequently appear collected in nodules or cysts and 

 are usually enclosed in a sort of connective tissue sheaths. Fig. 43 

 represents an eye stump of Palaemonetes, showing one of these 

 pigment depositions. Fig. 72 shows an outline section through 

 this stump from which the relation of the pigment to the normal 

 issues can be readily made out. Fig. 43 shows in detail the 



