24 UNIVERSITY OF MISSOURI STUDIES [212 



on during the summer. Morgan's entire series of experiments 

 was begun and ended within a month, while in no case does 

 Herbst report any definite regeneration to have appeared within 

 less than three months, and then not until after two or three 

 moults had taken place. 



In my experiments upon crayfish it has proved absolutely 

 true that nothing definite concerning the regeneration can be as- 

 certained until after a moult, although the length of time be- 

 tween the operation and the appearance of the regenerated 

 structure varies in individual cases very greatly. It is true that, 

 when only the distal portion of the eye is removed, an apparent 

 regeneration takes place in a very short time, but it is only a 

 partial restoration in size and not a true functional regeneration. 

 This point will be referred to again and more carefully consid- 

 ered. 



The eyes of crayfish have been operated upon at three dif- 

 ferent levels and at varying angles. First, a part of the cornea, 

 sometimes just the top, was cut away, and sometimes a portion 

 was cut from one side; second, the entire corneal surface was 

 removed; and, third, the whole or the greater part of the optic 

 peduncle was cut away. In the latter case of course, the optic 

 ganglion was either wholly or partially removed. 



The results obtained from these experiments will be dis- 

 cussed under two main headings; first, regeneration after re- 

 moval of a portion of the eye ; and second, regeneration after re- 

 moval of the entire eye. In all cases only one eye was operated 

 upon. I am unable to say how large a percentage of the indi- 

 viduals used in each case ever yielded results of value. Many of 

 them died before reaching the moulting period, and consequently 

 I found it impracticable to keep a record of any except those 

 that were killed for examination or those that exhibited notice- 

 able regeneration before dying. Owing to the rapid disintegra- 

 tion of the tissues no satisfactory results could be obtained from 



