NATURAL SCIENCES OP PHILADELPHIA. 271 



inheritance from a common stock, and which equally forbid the 

 idea of considering them as indications of affinity or likeness even 

 from a metaphysical point of view. 



Further Considerations. 



Among other characters supposed by various authors to justify, 

 or even render "too evident not to be immediately appreciated,"* 

 the relations of the Sirenians and even true Cetaceans to the 

 Pachyderm Ungulates, are the considerable relative size and co- 

 ordinate increase of special parts, "the thick and naked skin," 

 " the variable and irregular teeth," as well as station. The varia- 

 bility and wide range in size and concomitant development within 

 the limits of a strictly natural group is, however, evidence of the 

 little value of the character, the skin is not naked in any Pachy- 

 derms, and it is not obvious how irrelative variability in dentition 

 is indicative of affinity when it presents no other elements of 

 similarity for comparison. Finally, even conceding the value of 

 station as an element for the determination of ordinal affinities, 

 it is not " obvious" why the horses, the rhinoceroses, and allied 

 t3'pes, should be regarded as pre-eminently frequenters of rivers 

 and marshes. To the writer, at least, the affinities claimed are 

 not evident. 



Genealogy of Sirenians. 



The special relations among themselves of the Sirenians, at least 

 of those whose skeletal remains are in good part known, appear to 

 be tolerably evident, thanks to the labors of various zootomists, 

 but above all of Prof. Brandt." In Halitherium we have the most 



' " The relationship between the Cetacea [ Cete and Sirenia'] and the next 

 order ['^Parhyderma''''] that offers itself to our notice is too evident not to 

 be immediately appreciated. The thick and naked skin, the gigantic body, 

 the massive bones, the bulky head, and even the variable and irregular 

 teeth that arm the ponderous jaws, are all again conspicuous in the Pacht- 

 DERMATA ; and the river and the marsh, the localities frequented by the 

 latter, as obviously indicate the intermediate position which these animals 

 occupy between the aquatic and the terrestrial mamnialia." Jones's 

 (Thomas Rymer) General Outline of the Organization of the Animal King- 

 dom, 4th ed., 1871, p. 809, 2201. 



* Brandt (Johann Friedrich). SymbohB sirenologicte, [fasciculus I.,] 

 quibus praecipue Rhytince historia naturalis illustratur. .... (1845) 

 <;Memoires de I'Academie Imperiale des Sciences de St. Fetersbourg. 



