l88 Mary Isahelle Steele 



may be well to mention a fact that has been observed a number of 

 times. The regeneration of the new ommatidia never presents a 

 uniform stage of differentiation in any case whether or not all of 

 the old ommatidia have disappeared. In fact it may be possible 

 to select several stages from the same eye and sometimes two or 

 three stages from the same section. 



An eye thirty days after the injury, Fig. 6, shows some interesting 

 features in comparison with the one just described. From a 

 ventral view this eye shows no signs of remaining ommatidia and 

 from the dorsal side only a very few cones and facets are evident. 

 The upper part of the eve is transparent. Below this transparent 

 area are scattered patches of pigment representmg the remains of 

 the old eye. Sections show that no new ommatidia have been 

 entirely differentiated, that the retinular cells have differentiated 

 and are establishing connections with the optic ganglion, that new 

 cone nuclei are being separated from the hypodermal nuclei, that 

 on one side a few of the old ommatidia remain and that in the 

 tissues lying nearest the old ommatidia new cones are being 

 developed. The most striking feature presented by this specimen 

 is the clearness with which the connections between the retinulae 

 and the ganglion cells can be made out. These connections will be 

 discussed at length in the consideration of the detailed structures 

 of the regenerating eye. 



Fig. 17 shows the ventral view of a regenerating Palaemonetes 

 eye from a thirty-five day specimen. Examination of the dorsal 

 side shows that a large number of the ommatidia on that side 

 appear uninjured, the greater part of the injury being confined to 

 the ventral side as indicated by a surface examination. Sections 

 show, however, a gradation of regeneration from a stage in which 

 there is no signs of cone differentiation to the complete formation 

 of a new ommatidium. 



It was said above that hermit crabs regenerated an eye more 

 rapidly than either Crangon or Palaemonetes even in instances 

 where a considerable portion of the optic ganglia had been 

 removed. Figs. 5, 12 to 15 show regenerated eyes of hermit crabs 

 after one or more sections of the optic ganglion have been de- 

 stroyed. Fig. 12 had at least the distal division of the ganglion 



