HIGHWAY OF ANIMAL EVOLUTION 215 



Ne. 



?# *? J? 141$ 16 2718 1920 



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Ho. 



FIGURE 6. DIAGRAM OF TRIAXIAL GROWTH. A, from side; B, in median 

 longitudinal section; C, in cross section in the region of the ninth metamere. 

 Letters and numbers as in fig. 4. Arrows indicate main lines of conveyance, 

 locomotor, vascular, alimentary, and nervous. In B, the chief systems of 

 medianly located organs are indicated, showing their linear arrangement. 

 In C, bilateral symmetry, the lines of concentric growth, and the relation 

 to gravity are indicated. Note the repetition of metameric organs in the 

 middle region of the body and the decline of metamerism on the haemal 

 surface at either end. The figures are based on the arachnid type of growth. 



mentary, vascular, excretory, muscular, and skeletal. 

 (3) Maximum economy of locomotion. (4) Maxi- 

 mum internal diversity. (5) Maximum opportunity 

 for increase in volume without loss of these attributes, 

 or serious detriment to them. (6) Maximum opportu- 



