Regeneration m CoinpoiinJ Eyes of Crustacea 23 1 



hermit crabs and a like phenomenon has been noted for three 

 species of crayfish, Cambarus virihs and C. gracihs (Steele '04) 

 and the blind crayfish, C. Pellucidus testii (Zeleny '06). 



Widespread as the phenomenon appears to be, however, no 

 satisfactory explanation of the cause of such heteromorphic 

 regeneration has yet been suggested. Also an explanation of the 

 negative cases, that is, where no particular regeneration takes 

 place, is equally wanting. In the explanation of any phenomenon 

 it is essential that negative cases be taken into account before any 

 general conclusions are drawn. As has been pointed out above, 

 even among the hermit crabs where the heteromorphic appendages 

 appeared most frequently, in by far the majority of cases no 

 regeneration took place. There was in these experiments a single 

 series of hermit crabs in which nine out of fourteen individuals 

 regenerated a heteromorphic appendage. In the light of this, we 

 should perhaps be safe in concluding that for hermit crabs failure 

 to regenerate may often be due to external conditions. But this 

 would still explain nothing for Crangon and Palaemonetes. 



All of the Crangon experimented upon belonged to the same 

 series and were kept as nearly as possible under precisely the same 

 conditions. Yet but one out of the original twenty-two developed 

 an antenna-like appendage notwithstanding there were fourteen 

 others that lived as long or longer and moulted as frequently. In 

 so far as it was possible to determine the question, the physiological 

 activity of the fourteen that showed no regeneration was equal to 

 that of the one individual that did regenerate the appendage. 



Extensive series of Palaemonetes were operated upon at the same 

 time with the hermit crabs, and were kept under similar conditions. 

 Yet, as has been seen not one regenerated the antenna-like append- 

 age. From this it appears evident that, whatever variations in 

 results may be accounted for by differences in external conditions, 

 the primary answer to the question must be sought elsewhere. 



It may be objected that in operating upon the eye the entire 

 optic ganglion was not always removed. This, however, could 

 not be offered as an objection in every case. In all three of the 

 forms there were many instances in which not a vestige of the optic 

 ganglion remained, and yet no regeneration resulted. Besides 



