FIGURE 7. DIAGRAMS, CORRELATED WITH THE GEOLOGICAL TIME TABLE, 

 illustrating the growth of the triaxial system of gradient functions. The 

 chief architectural innovations are indicated as they successively appear 

 in the different classes of animals which probably form the more direct 

 ancestral stock of the higher vertebrates, these innovations attaining their 

 logical conclusion in man. 



The main events indicated are: (i) the rise and decline of metamerism, 

 or the increase in the number of metameres successively developed at the 

 tail end, their increasing destinction in the middle region of the body 

 (arachnids) and their gradual break down, or fusion with one another, 

 toward the head end and haemal side; (2) cephalization, or the con- 

 centration of a large number of bodily metameres, about 15-20, to form 

 the "head" in the higher classes (y.y.&z.z.) ; and (3) the coincident centrali- 

 zation and redistribution of the great systems of bodily functions. Note 

 the persistent reduction in the number of metameric organs performing 

 similar functions, or their combination into a single system, and their shift 

 of position to more fitting locations with the general increase in growth. 

 The chief functions centralized toward the head end are the nervous and 

 sensory ones (gustatory, visual, auditory, and olfactory). The locomotor, 

 L, excretory, ex, and sexual, centralize at the opposite end; and the respira- 

 tory, R, digestive, D, and circulatory, C, toward the centre of the body. 

 The assumed duration of geological time is indicated in ratios of million 

 year periods, M. 



