Regeneration iii CouiponnJ Eyes of Crustacea 187 



Fig. 3 represents the ventral view of a Palaemonetes eye ten days 

 after being injured. In this case also the injury extends across 

 the ventral side of the ommatidial portion. The pigment of the 

 broken down ommatidia can be seen scattered in flakes and 

 patches through the upper part of the eye. From the dorsal side 

 the eye appeared nearly normal but sections show that almost the 

 entire eye is in process of degeneration. 



The specimen represented in Fig. 4 shows a regenerating eye 

 nineteen days after the removal of almost all of the ommatidial 

 portion. It is readily seen that very little remains except the eye 

 stalk. The pigment patches are remains of the original eye. 

 Across the end of the stump the cuticle is wrinkled and folded, 

 indicating that comparatively little new tissue has been formed and 

 that the cuticle follows more or less closely the rough uneven out- 

 lines of the wounded surface. 



When the entire ommatidial portion has been removed or has 

 degenerated regeneration seems to be considerably slower than 

 when a large part of it remains uninjured. The two specimens 

 shown in Figs. 9 and 10 aff"ord a striking illustration of this fact. 

 Both of these eyes were operated upon at the same time. Each 

 animal moulted twice, the first time on the same day and the 

 second, a day apart. Both were fixed in picro-acetic at the same 

 time, thirty-two days after the operation. In Fig. 9 the injury 

 involved only the posterior ventral side, less than one-half of the 

 ommatidia. While in Fig. 10 the injury included all of the 

 structures lying distal to the basement membrane. Examination 

 of the sections shows new ommatidia completely differentiated in 

 Fig. 9 while in no part of Fig. 10 are they yet defined. 



The next specimen, Fig. 20, presents a rather striking appearance 

 and suggests immediately that the regeneration taking place is not 

 altogether of the normal type. This is a thirty-eight day specimen 

 and belongs to the same series of experiments as the preceding two 

 specimens. All of the part distal to the dark pigmented band is 

 regenerated tissue. The pigment consists chiefly of the remains 

 of the old retinulae. It is evident even from a surface view that no 

 ommatidia have developed. Sections show, however, that on one 

 side the diff"erentiation of cones is beginning (Fig. 69). Here it 



