Classification of Chordates: Protochordata 



391 



Fig. 301. A phylogenetic tree of the animal kingdom, showing its dichotomy 

 into Proterostomians and Deuterostomians. 



The number of species in a group cannot be exactly stated. Estimates made by 

 presumably equally good authorities may be at wide variance. The numbers given 

 in the "tree" have little significance beyond giving an approximate idea of the 

 relative size of groups. (Courtesy, Neal and Rand: "Chordate Anatomy," Phila- 

 delphia, The Blakiston Company.) 



