248 OUTLINES OF EVOLUTIONARY BIOLOGY 



is afforded by the whales, dolphins and porpoises (Figs. 101 

 and 161) with their extraordinary external resemblance to 

 fishes. The fore limbs, as we have already seen, are modified 

 to form paddles, but they retain the pentadactyl structure and 

 are thus totally different from the fins of fishes, which have 

 never reached the pentadactyl stage. The hind limbs have 

 completely disappeared, but vestiges of the limb bones and their 

 supporting girdle, which in some cases are found buried deeply 

 beneath the skin in the pelvic region (Fig. 101, f,p), still bear 

 witness to their former presence. The powerful tail fin has 

 obviously no real relationship to the tail fin of a fish, for it 



lies horizontally instead of 

 vertically. There are, of 

 course, no gills, as in fishes, 

 but the animal comes to 

 the surface to breathe air 

 by means of lungs. 



Not only is the whale 

 not a fish, but it belongs 

 to the group of vertebrates 

 most remote from fishes. 

 It is a warm-blooded 

 mammal, suckling its 

 young and exhibiting other 

 FIG. 103. The seven cervical Vertebrae characteristically mamma- 



of a Whale, fused together in one 

 Mass. (From Reynolds " V ertebrate 

 Skeleton.") 



li an features. It has seven 



. , 

 cervical vertebrae, a number 



which is curiously constant 

 throughout the mammalian series, but owing to the extreme 

 shortness of the neck these vertebras are all crushed together to 

 form practically a single bone (Fig. 103). In the giraffe we also 

 find seven cervical vertebrae, but they are all greatly elongated 

 in accordance with the enormous length of the neck (Fig. 104). 

 On the hypothesis of special creation we should certainly have 

 expected the whale to have fewer vertebras in its neck than the 

 giraffe, and we can only suppose that the number seven has 

 been inherited from some common mammalian ancestor. The 

 resemblance of the whale to the fish, in short, is simply due to the 

 fact that both have acquired the external form best adapted for an 

 active aquatic life. 



The winga of pterodactyls, bats and birds are equally good 



