34 UNIVERSALITY OF DEGENERATIVE EVOLUTION 



degeneration is the exopodite. On considering the 

 development of the various parts of this appendage, 

 it may be concluded that the exopodite has not 

 undergone the same modification as the endopodite. 

 It now remains to conclude this study of the 

 abdominal appendages by an ex- 

 amination of the first segment. 

 Immense variation occurs in the 

 female. Sometimes there are two 



FIG. 6. Astacus fluvia- . , 



tuts. Left appendage appendages, sometimes one or both 



of the 4th abdominal rir . 



segment of the female are missing i in any case the 



(3/1) : pr, protopodite ; 



<?w.,endo P odite (Huxley), existing organs are very small 

 (tig. 6). The protopodite (pr.) is small, the exopodite 

 is missing, and the endopodite (en.) is represented 

 by an imperfectly jointed thread. The appendages 

 of this first segment being no longer necessary, 

 atrophy, and, as has just been 

 pointed out, there is no regularity 

 or uniformity in the order of their 

 disappearance. In the male, the 

 appendages of this segment (fig. 7) 

 possess an unjointed rod (t) cor- 

 responding to the endopodite of the FlG 7 _ Astacus fluvia . 

 second segment, and this, rod 

 stretches out to a considerable 

 distance. The exopodite is missing, < Huxle y)- 

 and the articulations between the different parts 

 have disappeared. This may reasonably be regarded 

 as the result of degeneration, and confirms what has 

 already been said concerning the appendage of the 



