THE METHOD OF CREATION OF ORGANIC FORMS. I93 



tive structure co-exist. The loyigitudinal is, however, predomi- 

 nant in the Vertedrata, Mollusca, and Articulata, while the cen- 

 trifugal is greatly developed in the Ooelenterata and Radiata. In 

 none but the simplest forms are either of these modes to be found 

 alone. 



The centrifugal repetition, or addition, more nearly resembles 

 the mode of aggregation of atoms in inorganic or crystalline 

 bodies, and hence may be regarded as the inferior manifestation. 

 It implies that growth-force in this case conforms to a law of 

 polarity in exhibiting itself at equal distances from a center — 

 which is allied to ordinary molecular force, and independent of 

 the localizing influences of which higher organisms seem capable. 

 In centrifugal animals, then, the latter evidently plays an in- 

 ferior part. In Coelenterates and Radiates, however, the body 

 possesses a short longitudinal axis, in some (Asterias) very short, 

 in others (Holothuria) more elongate. The amount of com- 

 plication of centrifugal growth greatly exceeds the complication 

 in a longitudinal direction in all of these animals except the 

 Holothurida. 



It is now important to observe that great numbers of centrifu- 

 gal animals are sedentary or sessile ; while the longitudinal are 

 vagrant, moving from place to place. Many of the centrifugal 

 animals which wander, do not do so in the direction of their axis, 

 but sideways {Medusce). It is also proper to notice that not only 

 the movements of the muscles but also the direction taken by 

 the food is in the long axis. It is therefore to be concluded that 

 in longitudinal animals growth-force has assumed a more truly 

 animal type, and that this tendency has predominated over the 

 polar or molecular tendency. 



In most longitudinal animals, however, certain lateral portions, 

 limbs, etc., extend on each side of the axis ; and were the space 

 marked by their extremities, and the extremities of the axis, filled, 

 we would have the outline of a centrifugal animal. 



Before discussing the influences which have increased and lo- 

 cated growth-force, it will be necessary to point out the mode in 

 which these influences must necessarily have effected growth. 

 Acceleration is only possible during the period of growth in ani- 

 mals, and during that time most of them are removed from the 

 influence of physical or biological causes, either through their 

 hidden lives or incapacity for the energetic performance of life 

 functions. These influences must, then, have operated on the 



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