106 The American Naturalist. [February, 



acters. In both the cases mentioned the male will furnish 

 these rather than the female ; but in a few cases the female 

 furnishes them. The fact that both sexes do not present them 

 does not invalidate them, any more than the possession of dis- 

 tinct reproductive systems would refer the sexes to different 

 natural divisions. 



I have seen characters objected to as of little value because 

 they were absent or inconstant in the young. I only mention 

 the objection to show how superficially the subject of taxo- 

 nomy may be treated. So that a character is constant in the 

 adult, the time of its appearance in development is immaterial 

 in a taxonomic sense, though it may have important phylo- 

 genetic significance. 



II. Phylogeny. 



The formulation of a phylogeny or genealogy involves, as a 

 preliminary, a clear taxonomy. I refer to hypothetical phylo- 

 genies, such as those which we can at present construct are in 

 large part. A perfect phylogeny would be a clear tax- 

 onomy in itself, so far as it should go, did we possess one ; 

 and such we may hope to have ere long, as a result of paleonto- 

 logical research. But so long as we can only supply parts of our 

 phyletic trees from actual knowledge, we must depend on a 

 clear analysis of structure as set forth in a satisfactory taxo- 

 nomy, such as I have defined above. 



Confusion in taxonomy necessarily introduces confusion 

 into phylogeny. Confusion of ideas is even more apparent 

 in the work of phylogenists than in that of the taxonomists, 

 because a new but allied element enters into the formulation. 

 It is in the highest degree important for the phylogenist, 

 whether he be constructing a genealogic tree himself or en- 

 deavoring to read that constructed by some one else, to be 

 clear as to just what it is of which he is tracing the descent. 

 Is he tracing the descent of species from each other, or of gen- 

 era from each other, or of orders from each other, or what ? 

 When I trace the phylogeny of the horse, unless I specify, it 

 cannot be known whether I am tracing that of the species 

 Equus caballus, or that of the genus Equus, or that of 



