22 UNIVERSITY OF MISSOURI STUDIES [2 lO 



who have given special attention to the subject are Faxon ('8i) 

 and Bateson ('94). Bateson (1. c, p. 537), reports a crayfish 

 with three extra claws. Among thousands of crayfish that have 

 passed through my hands I have not found as many as a dozen 

 that presented any sort of deformity. At all events the species 

 of crayfish with which I am most familiar, viz., Camharus gra- 

 cilis, C. virilis, C. inimunis, and C. rusticus are unusually free 

 from deformities of any kind. 



7. EYES. 



As was mentioned in the historical summary, some earlier 

 observations have been made upon the regeneration of the eyes 

 of Decapods. Herbst, however, is the only experimenter who 

 has given any special attention to the subject. The results of his 

 work have already been discussed (pp. 5-9). Chantran ('73) 

 also gives a brief account of the process, but I have been unable 

 to procure his original paper. Morgan ('98) discusses very 

 briefly the regeneration of the eyes of the hermit crab. It seems 

 at least certain from Herbst's and Morgan's work that crabs and 

 shrimps are much more favorable forms for experiments than 

 crayfish. From their accounts I should judge that regeneration 

 takes place much more rapidly, in the hermit crabs at least, than 

 in crayfish ; and also that there is not nearly so much difficulty 

 in keeping them alive as I have experienced in the case of cray- 

 fish. Besides tlie usual difficulties which have already been men- 

 tioned, a large percentage of the individuals whose eyes had been 

 removed, died shortly after the operation. Death, in these cases, 

 I attributed to loss of blood and nervous shock. Fewer died 

 when only the corneal part of the eye was cut off than when the 

 whole stalk was removed, and small individuals usually seemed 

 more hardy than larger ones. The point of paramount import- 

 ance here, as in the case of the appendages, is to keep the crayfish 

 alive through at least one moult after the removal of the eye. 



