38 UNIVERSITY OF MISSOURI STUDIES [226 



nite answer. Yet, from an examination of the regeneration of 

 the eyes of crayfish, it may at least be said that there are certain 

 reasons for regarding the eyes as modified segmental append- 

 ages, and the heteromorphic structures which arise when the 

 entire eye is removed indicate strongly that this interpretation 

 is the correct one. 



One of the most significant points in this connection seems 

 to me to lie in the fact that the structure which is regenerated 

 is not always an antenna-like organ. For instance, the structure 

 represented in Fig. 30, PI. IV, shows no segments whatever but 

 has very much the appearance of the bud of an ordinary ap- 

 pendage before constrictions appear which mark the future 

 joints. And furthermore, the fact that the regenerated struc- 

 tures sometimes appear in an antenna-like form, sometimes 

 with one, sometimes with a pair of flagella, may point to a grad- 

 ual transformation of the typical appendage, the appendage in 

 its phylogony, having passed through an antenna-stage before 

 reaching the condition of an eye. 



There may be some objection to regarding this heteromor- 

 phosis as atavism on the ground that the regenerated structure 

 lacks a basal protopodite. This, however, might be explained 

 on the hypothesis of partial reversion. And, if it were possible 

 to keep the same individual alive long enough to remove suc- 

 cessively the regenerated structures, as can be done in other re- 

 generated appendages, there would probably finally be regen- 

 erated an appendage more nearly approaching the typical form. 

 However, Herbst, in some of his experiments, removed the 

 heteromorphic structure, both wholly and in part, and found that 

 a similar structure was always regenerated. In the shrimp, 

 Herbst found an indication of a segmented basal portion, but the 

 segments possessed no movable articulations. Although here 

 there was a nearer approach to an ordinary appendage than I 



