2l8 Mary Isahelle Steele 



for their failure to regenerate. There were among the hermit 

 crabs several parallels between those that regenerated an eye and 

 those that did not, so far as conditions were concerned. In a 

 series of fourteen hermit crabs that had the ommatidial portion of 

 the eye removed five regenerated an eye and nine did not. All 

 were kept as nearly as possible under the same conditions. The 

 part of the eye removed in the original operation was about the 

 same for each individual. All were operated upon at the same 

 time in the same way. Some of those that regenerated an eye and 

 some that did not moulted upon the same day after the operation. 

 Consequently the physical condition of these specimens were 

 apparently similar. 



Compare Fig. 13 and Fig. 21. Each of the hermit crabs from 

 which these figures were taken moulted twelve days after the 

 operation. The hermit crab from which Fig. 13 was taken was 

 killed at the end of thirty-eight days and the other at the end of 

 sixty-seven days. The latter lived nearly twice as long yet it 

 shows no signs of regeneration. More of the optic ganglion 

 remains in the stump shown in Fig. 21 than in Fig. 13. Again, 

 compare Fig. 15 with Fig. 21. The two crabs from which these 

 figures were taken were operated upon at the same time, moulted 

 approximately upon the same dates and were killed sixty-seven 

 days after the operation. The stump shown in Fig. 21 shows no 

 regeneration while the one shown in Fig. 15 has regenerated an eye 

 perfect in all of its details. 



The number of cases might be multiplied but these given are 

 sufficient to show the parallels presented by individual cases. 

 Instances of this sort are confined in great part to hermit crabs. 

 A number of shrimp, however, failed to regenerate even when the 

 optic ganglion was not mjured. The same is true for Crangon 

 which in several instances failed to regenerate normally even after 

 the removal of only a small part of the eye. 



In most cases sections of such eyes that did not regenerate show 

 no recognizable pathological conditions. In the case shown in 

 Fig. 21, however, there was found what seemed to be the beginning 

 of pathological pigment development. Externally there were no 

 signs of pigment formation. The regenerated tissue consisted of a 



