I 914 ] Taylor: Aquatic Adaptation in the Carnivora 491 



have existed in its evolution, namely, that toward shortening of 

 the limb, and that toward backward extension of the limb. The 

 first tendency has brought about the shortening of the femur, but 

 the second has resulted in the epipodials remaining rather long. 

 Distal dilation has resulted from an elongation and lateral spread- 

 ing of the digits. 



Elongation and distal dilation of the hind foot is differently 

 brought about in the sea-otter and seal. In the former the fifth 

 digit is the longest, the first being the shortest, and those between 

 grading regularly from one to the other. In the latter the first 

 digit is the longest, the fifth being next, followed by the second, 

 third and fourth. The region in which expansion would be ex- 

 pected to occur is the outside of the foot, that is, on its posterior 

 margin, the region of the fifth digit. In those aquatic animals 

 which exhibit hyperdactyly, it is often the fifth digit which is 

 split. The extension of the swimming membrane calls for the 

 extra support on the posterior margin. 37 



The foot of the sea-otter is of such a form that this extra 

 support is furnished through the fifth digit being longest. In 

 this connection the following facts might be regarded as indi- 

 cating that Latax is derived from a form near the existing river 

 otter. Lutra canadensis has the first digit shortest, second and 

 fifth about equal, the fifth a little the longer, and the third and 

 fourth about equal. A considerable elongation of the fifth, and 

 a slight lengthening of the fourth, would bring about the relations 

 existent in the hind foot of the sea-otter. 



STAGE OF EVOLUTION OF LATAX 

 Latax has probably already attained to as great a degree of 

 structural adaptation to life in the water as is possible without 

 some modification in function of some of the various parts. This 

 change in function would be conditioned by a change in habits. 

 Following out the suggestions already presented it is conceivable 

 that, by coming to feed on fish and pelagic cephalopods, thus 

 attaining greater independence of shore animals, the sea-otter 

 might, in time, become entirely pelagic in habitat. In such an 



» 7 Osburn, E. C, "Adaptive modifications," Ann. N. Y. Acad. Sci., 

 vol. 16 (1906), p. 456. 



