Regeneration in Conipoinul Eyes of Crustacea 225 



C PALAEMONETES 



Out of nearly three hundred Palaemonetes not a single individual 

 regenerated any sort of an appendage when all or nearly all of the 

 optic stalk was removed. It is true that more than 50 per cent of 

 them died from the operation or soon after. Often half or two- 

 thirds of a series died within twenty-five or thirty minutes after the 

 operation, and in some instances the proportion was still greater. 

 (See Table i.) Palaemonetes were by far the least resistant of any 

 of the forms operated upon. There were, however, over sixty 

 individuals that lived from twenty to one hundred and twenty- 

 four days and moulted from one to three times. 



Considering the results of these experiments it may be said that 

 Palaemonetes vulgaris does not regenerate an antenna-like append- 

 age in place of an eye. Herbst would, perhaps, insist that these 

 results were due to a lack of time or to a failure to remove all of 

 the optic ganglion. This latter objection in many cases could not 

 be urged. The eye stalk in Palaemonetes is long and the optic 

 nerve extends well into its base. And in these experiments the eye 

 was so completely removed that not even the vestige of a stump 

 remained. Consequently there was no possibility of leaving any 

 part of the optic ganglion. Part of the brain even was removed 

 with the eye in two series. In regard to the other objection 

 naturally there is no positive proof that results might not have 

 been different in a longer period of time. There are strong 

 reasons, however, for believing that time would have made no 

 essential difference. Chief among these reasons is the fact that 

 in the regeneration of any other organ Palaemonetes needs but 

 little more time than the hermit crabs and less time than Crangon. 

 In three parallel series of experiments upon the regeneration of the 

 first antenna after its total extirpation it was found that Palae- 

 monetes regenerates a first antenna as quickly and as perfectly as 

 either Crangon or hermit crabs. In another parallel series of 

 experiments upon the regeneration of the second antenna it was 

 found that Palaemonetes regenerates this appendage rather more 

 rapidly than either hermit crabs or Crangon. Palaemonetes may 

 regenerate a first or second antenna in about thirty days. Neither 



