228 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1936 



shell too short to allow them to extend. It is a most puzzling and 

 extraordinary flipper, which so far cannot be precisely correlated 

 with its "use." No less remarkable is the flipper of the humpback 

 {Megaptera). This is of enormous length ; in a female 491/2 feet long 

 it measured 16 feet. As with the typical rorquals the number of the 

 phalanges in the second and third digits have greatly exceeded the 

 normal three of the mammalia generally. They are relatively long 

 and slender, and shaped like a dice box. But here, as in the killer, 

 the ossified portions of the phalangeals are capped at each end by 

 an enormous mass of cartilage, and these, along the front, or pre- 

 axial border of the flipper, produce in the living animal the series of 

 notches found in no other whale. The largest of these is formed by 

 the cartilaginous mass at the end of the first digit which terminates 

 with strange abruptness. 



Very few of the Cetacea have retained all five digits. We find this 

 number in Platanista, and in the right whales. Naturally it is as- 

 sumed that it is the pollex, or first digit, which is missing. But the 

 flipper of the common rorqual {Bdlmnoptera physdlus) urges caution 

 in this connection. For with some constancy the terminal end of a 

 digit is found between the second and third of the existing digits, sug- 

 gesting that reduction has taken place by the suppression, or "squeez- 

 ing out" of the third digit, and not by the loss of the pollex. In all the 

 Cetacea the fingers lie embedded, as in a solid, fingerless glove, either 

 extended parallel witli one another or radiating. But in the right 

 whale the three first fingers lie parallel, and close together, while the 

 third and fourth stand wide apart, as seen at the right of plate 4. 



Some still hold that all the varied types of animals we know, fossil 

 and recent, have come into being through the agency of natural selec- 

 tion. But surely "natural selection" has not determined the absence 

 of cartilage, save for articular surfaces, in some flippers, and its 

 enormous development in others. We cannot invoke this agency to 

 explain the remarkable flippers of the killer whale and the humpback. 

 Again, what survival value can the notches on the flipper of the last- 

 named species have had ? If the humpback has survived in the strug- 

 gle for existence because of the peculiarities of the internal skeleton 

 of this limb, why have the ziphoids, living the same mode of life, and 

 in the same medium, survived with a totally different flipper? 



Make no mistake. The strange and apparently meaningless dif- 

 ferences in these several forms of flippers are the expression of the 

 effects of precisely similar stimuli on tissues of different inherent 

 qualities. Each has responded after its own fashion. 



Confirmation of this contention is surely to be found in the flipper 

 of the Ichthyosauri— reptiles, be it remembered— which lived millions 

 of years before the Cetacea came into being. Like the Cetacea, and 



