210 GENERAL SUMMARY. 



2. In all segmented animals the central nervous system is morphologically 

 identical. 



3. In all segmented animals the three primary axes of bodily growth have 

 the same relation to the neural axis, i.e., apical growth extends in a cephalo-caudal 

 direction parallel with the neural axis; transverse growth extends right and left 

 at right angles with the neural axis; and radial growth extends in an ovocentric 

 direction approximately at right angles to the other two. 



4. The three axes of morphological and functional differentiation are co- 

 incident with, and follow the same direction as the axes of growth. 



5. The axes of growth and differentiation lead in directions of diminishing 

 returns. 



6. In embryonic growth the ratio between the relative rate of apical and 

 bilateral growth, and the radius of the yolk sphere determines the relative time, 

 place, and conditions for the formation of the organs on the haemal or aboral 

 surface of the body. 



7. The volume of the yolk sphere has been the most important variable 

 factor in modifying the mode of growth and the form of the body in the segmented 

 animals. Its increasing volume in the rotiferphyllopod-arachnid phylum has 

 in the higher arachnids and in the vertebrates greatly exaggerated the differ- 

 ences between the neural and haemal surfaces, and has been the chief cause 

 of the linear distortion and profound modification of the haemal portions of the 

 cephalic metameres. 



8. In the phyllopod-arachnid-vertebrate phylum the body grows by the 

 spasmodic generation of new groups of metameres at the caudal end of the body. 

 The new metameres of each generation are at the outset unlike those of the 

 preceding generation. Each generation of metameres gives rise to one of the 

 primary functional and morphological subdivisions of the body. 



9. Cephalic organs and cerebral centers are laid down at the same time and 

 in the same order, each reflecting the condition of the other. The linear arrange- 

 ment of the principal functional centers in the arachnid brain was determined 

 by the historic order in which the principal subdivisions of the body were generated 

 during the phylogeny of the phyllopod-arachnid stock. The cephalo-caudal 

 order in which the principal functional centers are arranged in the vertebrate 

 brain indicates the historic order in which the corresponding peripheral organs 

 were evolved in the arachnids. 



10. The distribution of functions and organs is determined primarily by 

 the nature of apical growth and by the conditions under which it takes place. It 

 is subject to a progressive readjustment due to a give-and-take exchange between 

 the new and the old organs in response to the physical demands incident to in- 

 creased size, and to other conditions created by growth. The actual arrangement 

 has been worked out subject to the following factors: i. The necessary preced- 

 ence in functional activity; 2. priority in origin and the consequent preemption of 

 territory; 3. the demand for a location essential to effective action. 



