2o8 Mary Isahelle Steele 



being differentiated into ommatidia. Sections of this eye show a 

 considerable development of abnormal pigment. At one side are 

 seen a limited number of regenerating ommatidia that have failed 

 to differentiate normally. The arrangement of the abnormal pig- 

 ment is of a character frequently seen in short stumps but not 

 generally found where the injury, as here, has not involved the 

 optic ganglion. The probable cause of this abnormal pigment 

 deposition will be considered in another section. The point of 

 chief interest here is that we find two sorts of development going 

 on side by side, one region developing normal structures and a 

 contiguous region developing abnormal structures. 



Another similar, though rather more exaggerated, case is fur- 

 nished by a small hermit crab (Fig. 25). The eye had been in- 

 jured before the animal was brought into the laboratory. No moult, 

 however, had taken place since the injury. About two weeks after 

 being brought into the laboratory the crab moulted and three days 

 later was killed. Fig. 25 represents the ventral view both of the 

 mjured and uninjured eye three days after the moult. It is seen 

 that the injury involved the whole ommatidial portion and appar- 

 ently a part of the optic ganglion. The distal surface of the 

 regenerating eye presents a very irregular outline. On the inner 

 border a peculiar protuberance has developed and two separate 

 pigment areas are apparent. The upper of these two areas 

 suggests that small ommatidia have been regenerated. Externally 

 the lower pigment mass suggests no probable explanation of its 

 character. 



Sections of this eye show a number of interesting points. In the 

 first place it is demonstrated that the upper and smaller pigment 

 area belongs to the retinulae of small but almost completely 

 developed ommatidia. All the structures of a typical ommatidium 

 have been differentiated with the exception of the corneal facets 

 and the spindle shaped enlargement at the base of the rhabdom. 

 The lower pigment area is an abnormal pigment deposition similar 

 to the preceding case. 



The protuberance developed on the inner border of the eye 

 seems also to be formed of abnormal tissue. Its interior is entirely 

 made up of a loose irregular network of tissue containing a number 



