INADEQUACY OF NATURAL SELECTION, ETC. 661 



by the aphides they are supplied with sweet substance by the 

 ants among which they parasitically settle themselves. How 

 easily the subjugated ants may fall into the habit of feeding 

 them, we shall see on remembering that already they feed not 

 only larvae but adults individuals bigger than themselves. And 

 that attentions kindred to these paid to parasitic ants may be 

 established without difficulty, is shown us by the small birds 

 which continue to feed a young cuckoo in their nest when it has 

 outgrown them. This advanced form of parasitism grew up 

 while there were yet only perfect males and females, as happens 

 in the initial stage with these New Zealand ants. What further 

 modifications of habits were probably then acquired ? Frem the 

 practice of settling themselves where there already exist colonies 

 of aphides, which they carry about to suitable places in the nest, 

 like Tetramorium, other ants pass to the practice of making ex- 

 cursions to get aphides, and putting them in better feeding places 

 where they become more productive of saccharine matter. By a 

 parallel step these soldier-ants pass from the stage of settling 

 themselves among other ants which feed them, to the stage of 

 fetching the pupae of such ants to the nest : a transition like that 

 which occurs among slave-making human beings. Thus by pro- 

 cesses analogous to those we see going on, these communities of 

 slave-making ants may be formed. And since the transition 

 from an unorganized social state to a social state characterized 

 by castes, must have been gradual, there must have been a long 

 interval during which the perfect males and females of these 

 conquering ants could acquire habits and transmit them to 

 progeny. A small modification accounts for that seemingly- 

 strange habit which Professor Weismann signalizes. For if, as 

 is observed, those ants which keep aphides solicit them to excrete 

 a supply of ant-food by stroking them with the antennae, they 

 come very near to doing that which Professor Weismann says the 

 soldier-ants do towards a worker " they come to it and beg for 

 food : " the food being put into their mouths in this last case as 

 almost or quite in the first. And evidently this habit of passively 

 receiving food, continued through many generations of perfect 

 males and females, may result in such disuse of the power of 

 self -feeding that this is eventually lost. The behaviour of young 

 birds, during, and after, their nest-life, gives us the clue. For a 

 week or more after they are full-grown and fly about with their 

 parents, they may be seen begging for food and making no efforts 

 to recognize and pick up food for themselves. If, generation 

 after generation, feeding of them in full measure continued, they 

 would not learn to feed themselves : the perceptions and instincts 

 implied in self-feeding would be later and later developed, until, 

 with entire disuse of them, they would disappear altogether by 

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