190 GENERAL EVOLUTION. 



Centrifugal. 



' More bilaterally { n ^ ^.'^ ^. ^ 

 symmetrical. '] Only bilateral. 



Longitudinal antero-pos- -< 

 terior and bilateral. 



More antero-pos- j Only antero- 

 teriorly. ( posterior. 



( In plane. 

 Centrifugal. •< 



( In globe. 



D. On Growtli-Force. 



From such examples as those that precede, but more especially 

 from the last, it seems necessary to believe that there resides in 

 organized matter, and in its most unmodified representative, the 

 nucleated cell, an affection which displays itself in repetition. 

 This phenomenon reduced to its lowest terms, may mean cell-divis- 

 ion only, but the proof is only clear in cases of gi'owth proper. 

 This affection displays itself in very slow or more rapid repetitions 

 — cell-division in growth occurring rapidly, while its recurrences 

 at rutting seasons in the development of horns, feathers, etc., are 

 separated by long intervals of time. In acceleration these repeti- 

 tions occur with increased rapidity, i. e., in the adding of more 

 structures during the same growth periods, while in low types its 

 repetitions are few and therefore slow. 



What is the relation of cell-division to the forces of nature, and 

 to which of them as a cause is it to be referred, if to any ? The 

 animal organism transfers solar heat and the chemism of the food 

 (protoplasm) to correlated amounts of heat, motion, electricity, 

 light (phosphorescence), and nerve force. But cell-division is an 

 affection of protoplasm distinct from any of these ; although addi- 

 tion to homogeneous lumps or parts of protoplasm (as in that low- 

 est animal, Protamceha of Hseckel) should prove to be an exhibi- 

 tion of mere molecular force, or attraction, cell-division is certainly 

 something distinct. It looks like an exhibition of another force, 

 which may be called groiuth-force. It is correlated to the other 

 forces, for its exhibitions cease unless the protoplasm exhibiting it 

 be fed. 



Professor Henry i^ointed out many years ago that this must be 

 the case, basing his belief on the observed phenomena of growth in 

 the potato, and in the Qgg. The starch of the potato weighs much 

 more than the young shoot of cellulose, etc., into which it has been 

 converted by growth-activity, so that a portion of the substance 

 of the tuber has evidently escaped in some other direction. This 



