SYMBIOSIS AND THE BIOLOGY OF FOOD 269 



larvae — including brothers and sisters — constitute the normal 

 diet. It is impossible to keep two larvae together in one small 

 vessel, as one attacks and kills the other within a few hours. 

 Even when I gave a tub to four specimens only one survived 

 after a few weeks, so that in a small loch, where at least some 

 thousands of these larvae hatch out, the death-rate must be 

 enormous." 



Now take the case of the honey-ants. " These ants," 

 says Mr. P. Leonard, in the Scientific American, Supp., Dec. 9, 

 1 91 6, " do not display such a wolfish eagerness to acquire any 

 chance scraps of food as is shown by other species, who live 

 from hand to mouth." Mr. Leonard goes on to say that, whilst 

 among the solitary insects, such as the flies, the moths, and 

 beetles, only a very small percentage of their numerous off- 

 spring ever reaches maturity, owing to paternal neglect, amongst 

 ants, under favourable conditions, the infant mortality is 

 practically nil. We are further told : " The ants have shown 

 the possibility of a perfect communal life, and have proved 

 that individuals can be incited to the maximum of effort with 

 the minimum of personal advantage, and that the little states 

 based upon unselfish sisterhood are supremely fitted to survive 

 in the struggle for existence." 



Mr. Balfour Browne's comparison of a carnivorous with a 

 herbivorous, or at least omnivorous, species of water-beetle 

 almost literally bears out the truth that you cannot make a 

 silk purse out of a sow's ear, i.e. by the method of perpetual 

 in-feeding. Whilst the carnivorous beetle lays its eggs singly 

 in holes pierced by it in the living vegetation, the herbivorous 

 beetle builds an elaborate silken cocoon, which floats in the water 

 and contains the eggs. 



We have seen that one result of the operation of Symbiosis 

 is to make the conditions of existence on our globe increasingly 

 favourable for those which are inclined to reciprocity. More- 

 over, the presence of industrious organisms tends to raise the 

 level of organic life much in the same way as the presence of a 

 thrifty class of citizens tends to raise the level of the socio- 

 political life. I employ the term symbiotic momenta in order 

 to indicate the power for good and for an ampler life engendered 

 by Symbiosis. These momenta in their entirety constitute, I 

 believe, an important evolutionary principle, namely, that of 

 " Symbiogenesis," by which I mean the direction given to 

 evolution by the long-continued operation of Symbiosis in 

 the production of higher forms of life, and in the more complete 

 development of beneficial relations between them. I consider 

 that the terrestrial conditions of life, for instance, are more 

 favourable than aquatic to the advance of Symbiosis, owing 

 to greater security and better opportunities for mutuality. 

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