Wilder.] 310 [Jime22 > 



ception is equally inexplicable with those of the vertebrae, since that 

 animal shows comparatively little more affinity with the marsupials, 

 than the sloth shows to the birds. 



Again, it is stated by Argyll (204, 223) that the number of tail 

 and wing feathers is constant throughout the Trochilidae, although 

 430 species are already known. 



Finally, the constancy in the number of mammalian digits is so ab- 

 solute, that not only do we exclude from the category all " sixth fin- 

 gers and toes," but we give no heed to the ossicle which projects from 

 the ulnar border of the carpus in Chelone (63. 1, 173) and in many 

 Cetacea (63, 2, 427), and call it "pisiform," although it looks as much 

 like a digital metacarpal as some which are generally accepted as 

 such; and, indeed, so convinced are we that five is the maximum 

 normal number of these parts, that we hardly wonder to find that the 

 required expansion of the manus with the mole and the Yapock opos- 

 sum is gained, not by the addition of a sixth digit, but by the exces- 

 sive development of a carpal ossicle. 



We must admit, therefore, that numerical composition means 

 something ; perhaps more in some cases than in others ; how much it 

 means is difficult to determine; probably, however, not as much as 

 relative normal position. 



The following citations from authors are sufficient to show the 

 present obscurity of this subject. 



"The examination of the skeleton (of fishes) has led to the conclu- 

 sion that the number of vertebras is another character of great 

 importance for the distinction of families; but whether it has any 

 bearing of still greater import, cannot be exactly determined at pres- 

 ent. 1 



Owen says, (63, 1, 42), "The number of trunk vertebras is useful 

 as a specific character in Icthyology." 



Agassiz writes as follows (200, 4, 64), respecting the zoological im- 

 portance of this attribute with radiates; " I would remind the reader 

 of the little value which numerical differences undoubtedly have in 

 this question, notwithstanding the constancy of the number of parts 

 in most of the radiates ; for though the number five is the typical 

 number among echinoderms, there are crinoids and starfishes and 

 even echinoids, with four and six spheromeres, and others with 

 an unusually large number; and though the number four and its 



1 Gunther; Cat. of Acanth. Fishes, 1861, Preface. 



