Reaction and Environment 177 



niy present purpose to penetrate beyond those precincts into the 

 realms of philosophy. We have to do with an ultimate biological fact, 

 with a fundamental property of living matter, which governs and 

 includes all its other properties. How may this property be stated ? 

 Thus : it is a property of living matter to react in a remarkable way 

 to external forces without undergoing destruction. The life-cycle, 

 of which the embryonic and larval periods are a part, consists of the 

 orderly interaction between the organism and its environment. The 

 action of the environment produces certain morphological changes 

 in the organism. These changes enable the organism to come into 

 relation with new external forces, to move into what is practically 

 a new environment, which in its turn produces further structural 

 changes in the organism. These in their turn enable, indeed necessi- 

 tate, the organism to move again into a new environment, and so the 

 process continues until the structural changes are of such a nature 

 that the organism is unable to adapt itself to the environment in 

 which it finds itself. The essential condition of success in this process 

 is that the organism should always shift into the environment to which 

 its new structure is suited — any failure in this leading to the impair- 

 ment of the organism. In most cases the shifting of the environment 

 is a very gradual process (whether consisting in the very slight and 

 gradual alteration in the relation of the embryo as a whole to the 

 egg-shell or uterine wall, or in the relations of its parts to each other, 

 or in the successive phases of adult life), and the morphological 

 changes in connection with each step of it are but slight. But in 

 some cases jumps are made such as we find in the phenomena known 

 as hatching, birth, and metamorphosis. 



This property of reacting to the environment without undergoing 

 destruction is, as has been stated, a fundamental property of organisms. 

 It is impossible to conceive of any matter, to which the term living could 

 be applied, being without it. And with this property of reacting to the 

 environment goes the further property of undergoing a change which 

 alters the relation of the organism to the old environment and places 

 it in a new environment. If this reasoning is correct, it necessarily 

 follows that this property must have been possessed by living matter 

 at its first appearance on the earth. In other words living matter 

 must always have presented a life-cycle, and the question arises what 

 kind of modification has that cycle undergone ? Has it increased or 

 diminished in duration and complexity since organisms first appeared 

 on the earth ? The current view is that the cycle was at first very 

 short and that it has increased in length by the evolutionary creation 

 of new adult phases, that these new phases are in addition to those 

 already existing and that each of them as it appears takes over from 

 the preceding adult phase the functional condition of the reproductive 



d. 12 



