216 SYMBIOSIS 



found that the oxidasic power of an organism varies with 

 magnitude of its respiratory exchanges (H. M. Vernon), which 

 is saying in other words that it varies with the organism's bio- 

 economic exchanges of services generally, i.e., as between 

 animal and plant. A symbiotic relation, we may take it, is 

 exceedingly favourable to auspicious, i.e., " normal " respiratory 

 exchanges, such as count in progressive physiological and, 

 ultimately, in anatomical transformation. It is obvious that the 

 chances of successful Symbiosis upon the land are greatly enhanced 

 if the candidate for the terrestrial life already practised a tolerable 

 degree of Symbiosis in the water. And we know that in what 

 may be styled " aquatic Symbiosis " respiratory exchanges play 

 a great role. The respiratory activities of Algae and other water 

 plants render the water hospitable for animals, many of which 

 Ccelenterates, Crustaceans, Molluscs live in close Symbiosis 

 with those plants, which, in turn, make use of the animal spare 

 products. 



We are told that : 



the 

 aich 



Looking broadly at the Mammals, we may say that the preservation 

 and elaboration of the inherited mobility of the fore-limb is an essential for 

 the culmination of evolution. We may also say that this preservation of 

 mobility must start very early, before ancestral mobility had become 

 lost in the development of stability ; and that the most successful Mammals 

 must, by some means or other, have preserved and stereotyped this 

 mobility almost at the outset of their mammalian career. Again, we may 

 say that two distinct lines have been followed. Some mammals have 

 perfected the new, and mammalian, demand for stability ; and others 

 have retained a primitive mobility in, at least, the fore-limb. It is the latter 

 which have been successsful and have become dominant. The problem 

 we are attempting to solve is : Why have some mammals retained this 

 primitive feature of mobility of the fore-limb, and why have these same 

 Mammals become more successful in the struggle of evolution ? 



My answer is that the " culmination of evolution " consisted 

 in the main in the perfection of the mutual relation between the 

 highest forms of animals and plants. To be a Mammal is ipso facto 

 to be emancipated from much that would otherwise militate 

 against high serviceability in Symbiosis. But there are different 

 degrees of Symbiosis, and some mammals, as we have seen, 

 have perfected Symbiosis more than others. They are those 

 which have been at once most serviceable to the higher plants, 

 and also most temperate in their habits. 



Broadly viewed, then, the two " paths " are determined by 





