12 HISTOKY OF CRUSTACEA. CHAP. II. 



rudiment nay, that it is sometimes present in youth 

 and disappears (although perhaps not without leaving 

 some trace) at maturity, as was found by Spence Bate 

 to be the case in Acanthonotus Owenii and Aiylus cari- 

 natus, and I can affirm with regard to an Atylus of these 

 seas, remarkable for its plumose branchiaa and that 

 from all this, at the present day when the increasing 

 number of known Amphipoda and the splitting of them 

 into numerous genera thereby induced, compels us to 

 descend to very minute distinctive characters, we must 

 nevertheless hesitate before employing the secondary 

 flagellum as a generic character. The case of Melita 

 Fresnelii therefore cannot excite any doubts as to 

 Darwin's theory. 



