302 



SGIENGE. 



[N. S. Vol. III. No. 61. 



the objection to show how superficially the 

 subject of taxonomy 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 phylogenetic sig- 

 nificance. 



II. Phylogeny. 

 The formulation of a phylogeny or gene- 

 alogy 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 phy- 

 logeny would be a clear taxonomy 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 paleontological 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 struc- 

 ture as set forth in a satisfactory taxonomy, 

 such as I have defined above. 



Confusion in taxonomy necessarily intro- 

 duces confusion into phylogeny. Confusion 

 of ideas is even more apparent in the work 

 of phylogenists than in that of the taxono- 

 mists, because a new but allied element 

 enters into the formulation. It is in the 

 highest degree important for the phyloge- 

 nist, whether he be constructing a genealo- 

 gic tree himself or endeavoring 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 genera from each 

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

 "When I trace the phylogeny of the horse, un- 

 less 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 the fam- 

 ily Equidfe. When one is tracing the phylo- 

 geny of species, he is tracing the descent of 

 he numerous characters which define a 

 species. This is a complex problem, and 

 but little progress has been made in it fi'om 



the paleontologic point of view . Something 

 has been done with regard to the descent of 

 some living species from each other. But 

 when we are considering the descent of a 

 genus, we restrict ourselves to a much more 

 simple problem, i. e., the descent of the few 

 simple characters that distinguish the genus 

 from other genera. Hence, we have made 

 much more progress in this kind of phylo- 

 geny than with that of species, especially 

 from the paleontologic point of view. The 

 problem is simplified as we rise to still 

 higher divisions, i. e., to the investigation 

 of the origin of the characters which define 

 them. "We can positively affirm many 

 things now as to the origin of particular 

 families and orders, especiallj' among the 

 Mammalia, where the field has been better 

 explored than elsewhere. 



It is in this field that the unaccustomed 

 hand is often seen. Supposing some phy- 

 letic tree alleges that such and such has 

 been the line of descent of such and such 

 orders or families, as the case may be ; soon 

 a critic appears who says that this or that 

 point is clearly incorrect, and gives bis 

 reasons. These reasons are that there is 

 some want of correspondence of generic 

 characters between the genera of the, say, 

 two families alleged to be phyletically re- 

 lated. And this want of correspondence is 

 supposed to invalidate the allegation of 

 phyletic relation between the families. But 

 here is a case of irrelevancy ; a generic 

 character cannot be introduced in a com- 

 parison of family characters. In the case 

 selected, the condition is to be explained 

 by the fact that although the families are 

 phyletically related, one or both of the two 

 juxtaposed genera through which the tran- 

 sition was accomplished has or have not 

 been discovered. The same objection may 

 be made against an allegation of descent of 

 some genus from another, because the phy- 

 letic relation between the known species of 

 the two genera cannot be demonstrated. I 



