7 HE EVIDENCE FROM DEGENERATION. 



353 



uses its modified feet as means for exercising the commissariat 

 and nutritive function. It is true that in some respects the adult 

 barnacle may be regarded as lower than the young, and therefore 

 as a degenerate being. Thus, it is lower when eyes, feelers, and 

 movements are taken into account. In other respects the adult may 

 be considered of higher organisation than the larva. These higher 

 traits we may logically enough suppose represent the special advances 

 which adult barnacle life has made on its own account. But, on the 

 whole, degradation and retrogression, if not so fully exemplified as 

 in the sacculina, is still plainly enough illustrated in barnacle history. 

 When we further reflect that even such high crustaceans as prawns 

 and allied forms begin life each as a "nauplius " or under an' allied 

 guise, we not only merely discover the common origin of all Crustaceans 

 in some form represented by the " nauplius " of to-day, but we also 

 witness the possibilities of development which have placed shrimps, 



FIG. 253. STYLOPS. 



(Fig. c shows the Stylops, in outline, within the body of the bee ; and Fig. b shows the Stylops 

 removed from the body of its host.) 



prawns, &c., in the foremost rank of the class, and which, conversely, 

 have left the barnacles and sacculinas, through the action of dege- 

 nerative changes, amongst the groundlings of the group. 



The assumption of a sedentary life, whether parasitic in nature, 

 like that of sacculina, or whether represented by mere attachment 

 and fixation to some inorganic thing, as in the case of the barnacles, 

 is therefore seen to operate in the direction of producing degeneration 

 of the animal's constitution. The tendency of such habit is towards 



A A 



