514 PATTEN— COOPERATION AS A FACTOR IN EVOLUTION. 



in direction, in content, and in speed ; solid bodies passing freely 

 in and out of the interior, and various other agents passing through 

 the walls from within outwards, and still different agents in the 

 opposite directions from without inwards; and (4) the character of 

 the structures produced along the lines and points of unlike condi- 

 tions would necessarily be unlike in texture and arrangement. 



This purely hypothetical case is cited to show that a progressively 

 diversified structure, reacting to the outside world at each succes- 

 sive stage in its own peculiar way, is an inevitable accompaniment of 

 growth, whatever the initial nature of the growing material may be. 

 That is, the form and the structure of such an organism are the 

 resultant products of an internal growth, which follows the lines of 

 easiest conveyance, and whose products accumulate along the lines 

 of least resistance. And the structure of the organism so produced 

 determines its reaction, as a whole, to the outside world. On the 

 cooperative value of that reaction depends its survival, or elimina- 

 tion, or the particular time or place, or sphere, of external environ- 

 ment within which it may endure. 



The obvious conclusion is that it is futile, and essentially unsci- 

 entific in method, to seek for the " explanation " of the structure and 

 function of an adult organism, in terms of germinal units, when the 

 only " explanation " to be found, if any, is in the analysis of a long 

 series of internal and external conditions, and when the things to be 

 explained are the last terms of the series, not the first. 



A body produced in the manner indicated above would have the 

 essential characters of a radiate animal, or one growing at equal 

 rates along its corresponding oral radii. Two principal modifications 

 of this method of growth might arise, due to some constant local 

 condition : namely increased tangential growth, or increased growth 

 along one radius. The former, if carried to an extreme, would tend 

 to form a spiral, or might revert to the original radial form (Fig. 

 I, F-I). Such a method of growth carries with it obvious mechan- 

 ical difficulties and no apparent advantages. The uniradial method, 

 if carried to an extreme, leads toward the bilateral type of apical 

 growth, and carries with it those great mechanical and economic ad- 

 vantages which have led to its retention and elaboration in all the 

 more highly organized animals (Fig. i, J-L). 



