230 Mary Isahelle Steele 



age shows that it should be regarded as a rudimentary first 

 antenna. The structure of the heteromorphic appendage regener- 

 ated by the hermit crab agrees in certain respects with the observa- 

 tions of Herbst upon the structure of the heteromorphic append- 

 ages regenerated by other forms. In other respects the obser- 

 vations made upon hermit crabs are not sufficiently extensive to 

 have any particular weight either way. The most significant 

 difference, however, between these observations and Herbst's is in 

 regard to the relation of the old optic nerve stump to the nerve 

 bundles extending through the appendage. In the heteromorphic 

 appendages regenerated by the hermit crabs there are several 

 cases in which there can be no doubt as to the continuity of the 

 optic nerve with the nerves in the appendage (Figs. 28, 34, 38). 

 Further, these are found in stages younger than any spoken of by 

 Herbst. 



The continuity of the optic nerve stump and the nerve trunk of 

 the heteromorphic appendage will be considered in all of its 

 aspects in the general consideration of the problem of such hetero- 

 morphic regeneration. 



E GENERAL CONSIDERATION OF REGENERATION FOLLOWING 

 REMOVAL OF ENTIRE EYE 



It has been seen in some cases that hermit crabs and Crangon 

 regenerate an antenna-like appendage in place of an eye. On 

 the other hand, the species of Palaemonetes used in this series of 

 experiments has never shown any indication of such regeneration. 

 In view of this, the question which naturally arises is why do we 

 not find antenna-like appendages growing from the eye stumps of 

 Palaemonetes vulgaris, when hermit crabs and Crangon kept under 

 the same condition do regenerate these structures, and when the 

 phenomenon is of pretty general occurrence among the Decapods. 

 Herbst has observed the development of an antenna-like append- 

 age from the eye stumps of a number of stalked-eyed Crustacea 

 belonging to different families. He has even secured a few cases 

 of this heteromorphosis in another species of Palaemonetes (P. 

 varians). Morgan ('99) was the first to make the observation for 



