TRANSFORMATION OF ORGANS OF ANIMALS 65 



6. Adaptation to swimming. Among mammals, 

 adaptation to swimming entails the functional dis- 

 appearance of the lower limbs, and the modification 

 of the fore-limbs into fins. 



This modification involves considerable degener- 

 ation. The alteration in the number of digits 

 varies ; the whale-bone whales have kept all five ; 

 in rorquals only four remain ; and, after a series 



FIG. 33. Skeleton of hand of 

 Chameleon. (After Cuvier.) 



FIG. 34. Chameleon. Skele- 

 ton of foot. (After Cuvier.) 



of intermediate conditions, the dolphin is evolved, 

 the fins of which are functionally two-toed. If the 

 Cetaceans vary as to the number of digits they ex- 

 hibit, they all have this character in common the 

 joints have disappeared. The arm no longer articu- 

 lates at the elbow, and neither the wrist nor the 

 phalanges are jointed. The simple stratum of 

 cartilage which takes the place of the true joints 

 allows of a slight movement of the various 

 segments, but not of true articular movement. 



