Wilder.] 332 [June 21, 



now all the above examples are peripheral parts, and the like ques- 

 tions never would have arisen with such a part as a vertebra. 



Putnam [Am. Nat., Jan. 1872, p. 26, note], mentions the slight tax- 

 onomic value of air-bladder, head-scales, barbels, ventral fins and 

 eyes, 'and Agassiz once figured fossil Crustaceans [Eurypterus remipes 

 and Pterygotus], as fishes on account of their external aspect. 1 



Packard 2 has recognized the unreliability of characters drawn 

 from peripheral and inconstant organs, like the mouth parts and 

 wings; and Owen himself seems to recognize the principle, "Judge 

 not according to appearances/' in the following paragraph : " The 

 prominent appearances which first catch the eye are deceptive; and 

 the less obtrusive phenomena which require searching out, more fre- 

 quently, when their full signification is reasoned upon, guide us to 

 the right comprehension of the whole." 3 



From the unpublished lectures on Selachians I again quote Agassiz: 

 " The Chimerse are generally separated from the other Selachians on 

 account of a single branchial fissure ; but as this is a variable charac- 

 ter, it should not set aside more internal characters." 



A zoological illustration of our proposition is given in the great 

 variety and discrepancy of the definitions of the vertebrate type; so 

 long as investigators regarded especially some one group with which 

 they were more familiar, and so long as they included in their defi- 

 nition of an abstract idea, the special structures which characterized 

 those minor groups (see Agassiz, 201, 213), so long they disagreed 

 among themselves, and failed to follow Nature; this is seen in the 

 difficulty which others have found in accepting Owen's archetype 

 skeleton as correct; for it is essentially a piscine skeleton, and 

 although the great anatomist holds that fishes depart least from the 

 vertebrate archetype (63, 1, 102), such a generalization involves 

 reasoning in a circle, and has been adopted by few (as Maclise, 23, 

 674-6 76). 



The Amphioxus is, without doubt, the simplest known vertebrate; 

 but it cannot be regarded as the material manifestation of the verte- 

 brate idea, since its structure presents positive characters by which 



Microscopic section of the tooth of Ceratodus has convinced Mr. Bicknellthat 

 it is " unsafe to found genera or even species upon the microscopical structure of a 

 single tooth or bone, although it has proved correct in many cases." Proc. Bost. 

 Sac. Nat. Hist., April 19th, 1871. 



2 Guide to the Study of Insects, p. 14. 



s Paleontology, p. 357. 



