28 THE APODID^. parti 



towards the ventral middle line might be expected to 

 bring the dorsal parapodia as well, at least far enough 

 round to allow them to assist in locomotion. There 

 is, further, no need to limit the functions of the dorsal 

 parapodia simply to locomotion, — they may at the 

 same time assist in capturing food. Starting from 

 the assumption that it was the habit of browsing 

 which first led to the transformation of the Annelid 

 into the Crustacean, the above is, in outline, the way 

 in which we should expect the Annelidan parapodia 

 to be gradually developed into Crustacean limbs. 



It is not possible in this place to bring forward at 

 once all the arguments which, we think, show that this 

 sketch of the rise of the Crustacean limbs out of 

 Annelidan parapodia is a fairly correct account of 

 what actually took place. One reason is, however, here 

 in place while discussing the limbs as a whole. It is 

 only in such primitive Crustacean forms as the 

 Apodidae and the Trilobites that we find the ventral 

 parapodia retained and functioning as jaws along the 

 greater part of the body, as we assumed for our 

 original Crustacean-Annelid ; the dorsal parapodia of 

 the same segments functioning, in the Trilobites, 

 purely as locomotory organs, in Apus both for 

 locomotion and for capturing food. In the higher 

 Crustacea we find a pronounced division of labour, 

 viz., the perfection of the ventral parapodia round 

 the mouth for mastication, and of the dorsal para- 

 podia in the rest of the body, either anteriorly for 

 seizing food, like the chelate limbs of the Decapoda, 

 or posteriorly for locomotion, like the ambulatory legs 



