178 On the Adaptation of Mammals to Aquatic Life. 



instance, as has been preserved with but little modification in 

 the Chelonia. All this is not found in the whalebone whales, 

 whose carpus consists of remarkably fewer elements. Where 

 changes do show themselves in the carpus they are never 

 cases of fission, but rather of fusion. This observation, which 

 we owe to Gegenbaur, is of universal application ; those carpi 

 are therefore to be regarded as the more ancient which exhibit 

 the greater number of component parts. These are the carpi 

 of the toothed whales. We therefore conclude from the 

 comparison of the structure of the carpus in the toothed and 

 whalebone whales that the former animals are the more 

 ancient. If we likewise take into consideration the difference 

 in the manner of the further development of the flippers, we 

 again arrive at the conclusion that the toothed whales were 

 developed from land-mammals at a much earlier epoch than 

 whalebone whales, and that therefore the two groups cannot 

 be directly related to one another. 



Our investigations into the structure and development of 

 the flippers have therefore yielded the same result as the 

 investigation of the integument. What were hitherto regarded 

 as resemblances and indications of phylogenetic relationships 

 are merely convergences which have arisen according to the 

 same developmental laws. 



With this the series of systems of organs which are modified 

 by adaptation to aquatic life is by no means exhausted, and 

 the studies which I have prosecuted on a tolerably compre- 

 hensive material into the dentition, the respiratory organs, &c. 

 contain much that is perhaps of more general interest. 

 Since these investigations, however, have not been entirely 

 concluded, I have confined myself in this paper to a couple of 

 systems of organs. From these the method of investigation 

 may at once be perceived. 



The earlier investigations for the purpose of elucidating the 

 phylogeny of the mammals to which 1 have directed atten- 

 tion have yielded contradictory results, since their proofs 

 were based on a series of common characters. By bringing 

 biology and physiology into the sphere of our observations we 

 have recognized these common characters as resemblances or 

 convergent developments, which have arisen through the 

 adaptation of originally dissimilar organs to new and precisely 

 similar conditions of existence. In the case which we have 

 been considering, the modification of the organs of the various 

 animals is controlled by laws of general application, laws 

 which are even partially attributable to mechanical principles. 

 Now when we thus betook ourselves to the investigation of 

 phylogeny from our altered standpoint, ecpaipped in this 



