219] REGENERATION OF CRAYFISH APPENDAGES 3 I 



removed April 9, 1901, and the crayfish moulted about six 

 weeks later. The great difference in size between the regener- 

 ating eye and the normal one, and the evident pigment spot at 

 the distal end of the former, are noteworthy. Figs. 36 and 37, PI. 

 II, shows sections of the regenerating eye. In Fig. 36, merely 

 the cuticular outline, the hypodermis, and the arrangerrjent of the 

 pigmented portion at the distal end are seen. The pigment 

 shows a somewhat systematic arrangement, as if ommatidia were 

 being developed. But the pigmented portion lies close under the 

 cuticle. There is nothing to indicate that crystalline cones or 

 corneal facets are being regenerated. The cuticle is equally as 

 dense and thick over the pigmented portion as over the remain- 

 der of the eye, and it is very noticeably thicker than the cuticle 

 over the corneal portion of the normal eye. Fig. 37 shows the 

 same features as Fig. 36, and in addition, a part of the optic gan- 

 glion (gl.). From this figure it will be seen that there is no 

 continuity between the optic ganglion and the pigmented struct- 

 ures, the latter being fairly well separated from the deeper parts 

 by a band of connective tissue. The position of the muscle fibres 

 (in) would seem to indicate that the connection between the 

 peripheral eye structures and the optic ganglion is being severed. 

 The ganglion-cells themselves have not the exact appearance of 

 those of the opposite, normal eye. Their outlines are not quite 

 so clearly defined and they are rather more irregular in size. 

 Yet the difference is not clearly enough marked to enable me to 

 decide whether or not the ganglion-cells of the regenerating eye 

 are actually degenerating. But at all events, an examination of 

 the entire series of sections gives no evidence whatever that re- 

 generation of the nervous portion of the eye has taken place. 



From the evidence presented by the last two specimens it is 

 hardly possible to conclude that a functional eye has been regen- 

 erated. On the one hand, the development of pigment has taken 



