Regeneration in Compound Eyes of Crustacea 207 



enon has, however, suggested itself. The differentiation of new 

 ommatidia appears to depend largely upon the reestablishment of 

 connections between the optic ganglion and the new tissue. That 

 such is the case is suggested by the fact that in regenerating eyes 

 the retinular processes reach the optic ganglion before the cones 

 begin to differentiate and before any pigment is deposited in the 

 retinulae. Further, according to Parker {loc. cit.) in the embryonic 

 development of the lobster's eye from the earliest beginning of 

 differentiation there is a connection between the ommatidial region 

 and the optic ganglion and this connection is never lost at any 

 stage in the development of the eye. Since the pigment appears 

 in the retinulse after they have formed connection with the ganglion 

 its presence in this stump (Fig. 36a) may be an indication that the 

 connections between the optic ganglion and the new tissues have 

 been formed and consequently that further development of 

 ommatidial structures has been initiated. 



This suggested explanation does not of course give any reason 

 why ommatidial development should begin on the ventral side 

 rather than elsewhere. The following explanation is suggested. 

 Cross and longitudinal sections of the normal eye stump show that 

 the optic ganglion extends somewhat nearer the surface toward 

 the anterior ventral side. On this account perhaps rudimentary 

 ommatidia have developed on the ventral side first because the 

 distance between the new tissue and the optic ganglion was shorter 

 so that nerve connections were more quickly established in that 

 region than elsewhere. 



Other cases of aberrant regeneration have also come under 

 observation. These, however, have been produced apparently 

 by pathological conditions. One or two of the more interesting 

 cases will be described. Fig. 19 represents dorsal surface views 

 of a Palaemonetes eye thirty-one days after the removal of the upper 

 part of the ommatidial portion. Eight days after the operation a 

 moult occurred. A second moult occurred fifteen days later and 

 it was seen that the greater part of the ommatidial structures had 

 disappeared. Fig. 19 shows a mass of pigment just distal to the 

 optic ganglion. Above this pigment there is a considerable area of 

 transparent tissue which shows no external evidence, however, of 



