THE ANCESTRY OF THE VERTEBRATES 



653 



says, thirteen neuromeres in the arachnid brain, but these do not corre- 

 spond with the number of metameres in the head. Arachnid and verte- 



Ms. a 



Br.C 



st.co. ..." 



Fig. 528. — Diagrams "showing the five characteristic body regions of arthropods, 

 and their progressive concentration to form the head of a vertebrate." A and B, 

 Insects; C, Arachnid; D, Vertebrate. The principal points illustrated are: The enlarge- 

 ment and concentration of the anterior cephalic neuromeres; the closure of the old 

 mouth and the formation of a new one; the transfer of locomotor organs from the 

 mesocephalon to the postbranchial metameres. (From Patten's "Evolution of Verte- 

 brates and Their Kin.") 



brate brains are also in essential agreement in the distribution of the main 

 fiber tracts. The fact that the arachnid has nothing comparable with 

 the vertebrate trunk makes it seem to Patten impossible to compare the 



