ADAPTATION TO ENVIRONMENT WAKDLAW 395 



immediate vicinity of living matter, of conditions resembling those 

 of its primitive state. From this point of view the whole story of 

 evolution is one of adaptation to environment. It is a history of 

 the mechanisms developed, of the subterfuges resorted to, of the 

 changes undergone by living matter to maintain essential characters 

 unchanged in a changing world. 



There seems to be a general agreement among biologists that liv- 

 ing forms originated in the sea. The chemical examination of 

 organisms supports this view. All the reactions of living matter 

 take place in aqueous solution. The ultimate units of structure, the 

 cells, even of the most highly developed land forms, still live in a 

 medium which bears certain striking resemblances to sea water. 



We have no direct means of knowing w^iat was the composition 

 of the aqueous medium in which living matter first made its ap- 

 pearance. It must, however, have been a dilute salt solution, but 

 of a composition differing materially from the sea w^ater of the 

 present time with respect both to the concentrations of and the pro- 

 portions between the various ions present. The water which first 

 condensed on the cooling surface of the earth would, in its course 

 downw^ards to the lower levels, begin to leach out the soluble mate- 

 rials with which it came into contact. The more soluble materials 

 w'ould dissolve more readily than the less soluble. As this leaching 

 action continued, the available supplies of the more soluble mate- 

 rials would diminish more rapidly than the available supplies of the 

 less soluble substances. It may be assumed, then, that the earlier 

 river waters, and the seas which they fed, were relatively richer in 

 these more soluble materials than the waters of later periods. 



During the period of their evolution in the w^aters of the seas, liv- 

 ing organisms have thus been exposed to a medium of continuously, 

 if slowly, altering composition. Does the study of the chemical 

 composition of the living organism of the present afford any evi- 

 dence that it has passed through these conditions? The individuals 

 of the more highly evolved species during their ontogeny pass 

 through a series of modifications of structure which summarize, as 

 it were, the stages through which the present form of the species has 

 been reached during the course of evolution. Macallum (1926) has 

 shown that there is reason to believe that just as the complex organ- 

 ism acquired certain structures at definite stages of its evolution, so 

 it has perpetuated certain of its chemical properties from remote 

 phases of the history of its forerunners. 



CHEMICAL AND MORPHOLOGICAL CHARACTERS 



At present the ontogeny of the chemical characters of organisms 

 is not known with anything like the detail wdiich is available with 



