ADAPTATION TO NEW FUNCTIONS. 



13 



from the first, able to offer a certain resistance to the common 

 motion of the whole body, and to serve as a fulcrum for the 

 movements of limited sections of the body in a way that might 

 certainly' be advantageous to the whole animal. Thus a gill 

 might be partially or whol'y transformed into an organ of 



Fig. 6. — G-ills, a, &, c, of Annelida ; d, of a, bivalve Mollusk. a, Navplianta celox (Greeff) 

 enlarged to three diameters, with broad gill-fins. 6, foot of Vanadis ornata (GreefE), 

 with two broad gill-fins, c, section of a segment of Eunice ; 67', the ramified giU- 

 appendages of the mdimentai'y foot, d, Mylilus eduUs^ with br, the gill-folds, and I, the 

 lips separated from them. 



locomotion, and accordingly we find in many Annelida gill- 

 bearing organs (fig. 6, a, b) which at the same time serve for 

 creeping or swimming, and which present that more specialised 

 form in which the functions of respiration and locomotion, 

 originally exercised simultaneously by the same organ, have been 



