1910.] The Cetacea: not related to Sirenia. 415 



auditory ossicles and of an internal ear, which all become profoundly modi- 

 fied for aquatic life; (5) the vestiges of the pelvis and hind limbs; (6) the 

 indications that the testes were formerly extra-abdominal and have been 

 withdrawn secondarily into the body cavity in adaptation to aquatic habits; 

 (7) the significant vestiges of the naso- and ethmoturbinals which indicate 

 that the reduction of the olfactory organs is only an extreme adaptation to 

 aquatic life, a process seen in less advanced stages among the Sirenia and 

 Pinnipedia. 



Hardly less clear, as Weber says (1904, p. 581), is the evidence that the 

 terrestrial quadrupedal forefathers of the Cetacea were true Placentals. 



The Cetacea not related to the Sirenia. The nearer affinities of the Cetacea 

 can best be treated after the claims of the Sirenia and Pinnipedia to this 

 relationship have been shown to be based upon purely convergent adapta- 

 tions. It would hardly be necessary to refer at this date to the old idea that 

 the Cetacea are genetically related to the Sirenia if it had not been defended 

 by two such eminent naturalists as Dr. Theodore Gill (1873, pp. 272-273) 

 and Professor Haeckel (quoted by Beddard, 1902, p. 120). Even if there 

 were no palseontological data bearing on the subject, the thorough review 

 of the morphology of the existing Cetacea and Sirenia given in Weber's 

 'Saugetiere' (pp. 552-580, 727-738) offers convincing evidence that the 

 marked resemblances between the two orders are entirely adaptive. Even 

 aside from the very conspicuous differences in the dentition and digestive 

 apparatus, the two orders are separated by profound differences in the whole 

 architecture of the skeleton, especially in the skull, lower jaw, scapula and 

 fore-limb bones; while equally striking differences (Weber, 1904, p. 739) 

 obtain in the brain, male organs, teats, etc. 



Dr. Gill holds that the detailed relations of the vestiges of the hind limbs 

 and tail in the two groups are so distinctly similar that they must imply a 

 relatively near kinship, because they can scarcely be conceived as being 

 altogether the result of convergent evolution. But in view of the cumulative 

 evidence against such a genetic relationship, that is precisely the conception 

 we are constrained to adopt. The "araphibiotic" ancestors of both Sirenia 

 and Cetacea doubtless had long and very heavy tails and small hind legs, and 

 as each group became more thoroughly aquatic the tail increased still more 

 and the hind limbs grew smaller and sank deeper into the integument. The 

 caudal "flukes" are in each case purely dermal appendages and bear of 

 course no homological relation whatever to the somewhat similarly appearing 

 hind flippers of the most advanced Pinnipedia. And when the palseonto- 

 logical record is appealed to it is seen that the Sirenia (p. 407) appear to 

 approach the Proboscidea, while the Cetacea (as shown below) approach the 

 Insectivore-Carnivore series. 



