518 PATTEN— COOPERATION AS A FACTOR IN EVOLUTION. 



in their time and space relations to the whole, are alike. In the 

 apico-bilateral plan, there are six unlike sides, and no two points in 

 the whole body are exactly alike. 



It is this greater diversity in local conditions, capable of infinite 

 expansion, that ultimately creates in the higher, segmented animals 

 the greater diversity in organic products so essential to cooperation 

 and the subdivision of labor. 



At the same time it will be observed that the location of the 

 various organs fixes the location of the points of intake and discharge 

 of special commodities thereby establishing a certain necessary order, 

 or sequence of events, in the passage of these commodities through 

 the three great channels of conveyance. 



But a linear arrangement of many similar organs, so character- 

 istic of primitive metamerism, would not, in the more voluminous 

 stages of the higher animals, give fullest expression to the latent pos- 

 sibilities of apical, bilateral growth. That is brought about by the 

 gradual breakdown of metamerism, most clearly marked at the 

 cephalic end, and chiefly due to the reduction in the number of 

 multiple parts and to the concentration of functions according to 

 a definite linear order at those points best fitted for the performance 

 of their function. That is to say, in the rearrangement of organs 

 that inevitably follows increase in volume, or in the " competition " of 

 organs for position, each function, as in a growing, well-organized 

 factory, tends to become established in that place in the system where 

 it thrives best, or cooperates best, and for that reason is best able 

 to perform its function. And this tendency will be perpetually 

 operative because of the greater cooperative and creative value of its 

 service to the whole organism when it is so placed. But any arrange- 

 ment of functions must be subject to the previously established fun- 

 damental order of inflow and outflow through the three great chan- 

 nels of exchange: nervous, alimentary, and vascular; to the mechan- 

 ical requirements of organic and bodily movements ; to the inherent 

 limitations in the tensile strength of protoplasm ; and to its powers 

 of resonant response. 



The history of the evolution of the arthropod-vertebrate stock, 

 covering a period of many millions of years, is chiefly the history of 

 the growth of old organs, the addition of new ones, and the per- 



