COMPARATIVE ANATOMY 



century, and called the Linnaean, or binomial, system. Thus all birches 

 are called by their Latin name Betula, and that is their genus. White, 



A PHYLOGENETIC TREE OF THE ANIMAL KINGDOM. 



Fig. I. — A phylogenetic tree of the animal kingdom, showing the dichotomy of 

 animals into Proterostomians and Deuterostomians. The former reach their evolu- 

 tionary climax in insects, the latter in chordates. 



yellow, and black birches are therefore respectively, as species, Betula 

 alba, Betula lutea, and Betula nigra; but the American white birch is 

 Betula papyrifera, that is, the paper birch; and the common gray birch 



