ANIMAL AFFINITIES 293 



obviously the direct action of the environment is to be reckoned 

 upon in ontogenies — and environmental changes consequent on 

 adaptive behaviour, migrations, etc. Plainly the establishment 

 of homologies from comparative-embryological studies may be 

 fallacious unless it is accompanied by experimental-embryological 

 investigations. 



97«. Phylogenies. Rational classifications thus suggest 

 phylogenies. A phylogeny is a formal statement that indicates 

 what have been the lineages, or descents, or blood-relationships 

 of large groups of organisms. Thus the classification of the 

 vertebrates given above may thus be restated. 



CifcLostomatcu Amphihiou ^P^^^^ 



AcrojiiatcL ""' " 



Saupopsida. 



—Ichthyops idbob 



^- -(jTUXthoStOTTWdtcL 



'Craniatcu 



Prirrutvue 

 chordjodxL 



Fig. 37. 



Here the root, and the divergences of the vertebrate stock, and 

 the facts on which these are deduced are just the same as in the 

 tabular classification, but the graphic w^ay of presenting the facts 

 suggests descent. 



The statement, nevertheless, is not to be regarded as a 

 phylogeny, or '' genealogical tree." Presently we shall see that 

 there *' ought to be " an actual historical record of such a phylo- 

 geny in the data of paleontology. That record, however, is 

 exceedingly imperfect in so far as it ought to present a general 

 vertebrate phylogeny and the data of morphology are absolutely 

 essential in constructing it. But imperfect as it is the paleonto- 

 logical record enables us to write the above phylogeny in a very 



