2G2 PROCEEDINGS OF THE ACADEMY OP 



ON THE AFFINITIES OF THE SIRENIANS. 

 BY THEODORE GILI^, M.D., PH.D. 



There exist, among the placental mammals, several well-defined 

 groups combined together and differentiated from all others by 

 the common character of atrophy, or entire want, of the posterior 

 members as well as pelvis, a pisciform shape, and adaptation for 

 habitual life in the water. These common co-ordinated characters 

 have been supposed by most zoologists to indicate close affinity. 

 A few, however, have considered them to be an insufficient index, 

 and recognizing that one of these groups was more isolated than 

 the others, and its members provided with a less abnormal skull, 

 and with a dentition and intestinal canal adapted for a vegetable 

 regimen, have approximated that group to the Pachyderm Ungu- 

 lates. Such zoologists seem insensibly to have been influenced 

 more especially by teleological considerations (adaptation for vege- 

 table food and complexity of the intestinal tract), and size. 

 Appreciating the vague (and very vague) similarit}'^ between the 

 groups in question (the Sirenians) and the hoofed mammals, 

 coincident with a comparatively large size (and thus contrasting 

 with the other herbivorous mammals), and further struck with 

 the agreement of the Sirenians with the hoofed mammals (Pachj^- 

 derms) distinguished by the negative character of want of a 

 compound stomach, they have combined the two into one order. 

 Unwilling, however, to confess or even admit to self, the influence 

 of such considerations, the d p?'iori conclusion reached has been 

 attempted to be substantiated by a selection of characters sup- 

 posed to be common to forms of the two groups, while no exclu- 

 sive diagnosis has been framed for the common group. But so 

 strong has been the prepossession, in favor of the view of the 

 affinities of the group in question, that it permeates and is felt in 

 systems where it is not avowed, and tliis influence is evident in 

 works of the latest writers. 



Probability of Common Origin. 



It is far more credible, in the opinion of the author, that the 

 ordinary Cetaceans and the Sirenians are derivatives from a 



