Regeneration in Compound Eyes of Crustacea 219 



heavy cuticle, a hypodermis and some loose strands of tissue 

 extending from the hypodermis to the distal end of the stump of 

 the optic ganglion. Grouped at the end of optic ganglion stump 

 and scattered in the loose tissue above it were a few cells of the 

 characteristic pigment-secreting type. But none of these cells 

 had yet become densely filled with pigment (Fig. 75^). It seems 

 rather improbable that so little abnormal tissue m which scarcely 

 any secretion of pigment had taken place could have been the sole 

 cause in the prevention of normal regeneration. Particularly is 

 this true when it is remembered that instances have been observed' 

 in which practically complete ommatidia were regenerated in eyes 

 containing great masses of abnormal pigment (Figs. 19, 25). 



VI Regeneration After Removal of the Greater Part 

 OR All of the Optic Ganglion 



There now remains for discussion those cases in which the 

 whole or most of the eye stalk was removed and consequently 

 either all or the greater part of the optic ganglion. Palaemonetes, 

 Crangon and hermit crabs will each be considered independently 

 since the differences presented by them are such as to require 

 separate treatment. 



A HERMIT CRABS 



Of a total of sixty hermit crabs operated upon twelve died as a 

 result of the operation, a loss of 20 per cent as against 55 per cent 

 of the Palaemonetes after a similar operation. Thirty-six of these 

 remaining crabs moulted from one to three times and lived from 

 twenty-three to one hundred and ninety-four days. These thirty- 

 six crabs fall into two groups: those that regenerated an antenna- 

 like appendage in place of an eye and those that showed no particu- 

 lar regeneration. 



/ Regeneration of Heteromorphic A ppejidages 



Ten crabs in all regenerated an appendage from the old eye 

 stump. In but one case was more than thirty-two days required 

 for the appendage to become apparent. All of these appendages 

 are very small none exceeding in length the normal eye stalk. It 



