240 SYMB10GENESIS 



may he termed a mechanical disadvantage ; but it is rather an 

 evolutionary disadvantage of which the above is only a con- 

 comitant, and it has been brought about by the predatory 

 habits which have driven these mammals to an aquatic life with 

 consequent siirrender of biological symbiosis as carried on by 

 biologically useful animals, and some of them, e.g., the whales, 

 just like certain monstrous terrestrial carnivora, have grown 

 body and digestive apparatus antithetically to brain an anti- 

 thesis which is the natural outcome of their bio-economic 

 retrogression. The reason why there is such a great blood supply 

 to the grey matter of the brain," Dr. F. W. Mott tells us, " is 

 that important bio-chemical processes occur there, constituting 

 the physiological basis of mental activity." All "supply," 

 however, is in the long run conditional upon symbiosis, and if 

 in the case of the monstrous carnivora (suffering from a long- 

 standing diathesis), eventually the brain shrivels, we must 

 conclude that their vital Bio-Chemistry has deteriorated pari 

 passu with the growth of their antibiotic behaviour. 

 Experimental verification of the fact that the ingestion of 

 inappropriate nitrogenous food materials has decided patho- 

 logical effects upon the brain will be forthcoming in the next 

 chapter. It is true Darwin concedes that a carnivorous 

 quadruped may better succeed in survival by " becoming less 

 carnivorous," which we found indeed paralleled by the 

 case of the Convoluta and of Dendrocygna, although Darwin 

 only refers to the greater possibilities of food-supply (when 

 not too strictly limited to flesh food), and seems scarcely aware 

 of the wider (symbiogenetic) application of his statement. 



On the other hand it is among symbiotic cross-feeders 

 (i.e., non-parasitic vegetable feeders), aided by the forces of 

 biological symbiosis, that we find striking evidences of the 

 evolutionary ascent from aquatic to aerial respiration. The 

 amphibians figure very conspicuously in this category. We 

 have in the tadpole, feeding chiefly on algae, an instance of a 

 survival of cross-feeding habits which must have been largely 

 responsible in the past for the production of that physiological 



