BIOPSYCHOLOGICAL 613 



enregistration. They are on different lines from intelligent behaviour, 

 which implies initiative and tentative. An instinctive action is like 

 a reflex action, but at a higher level, and with more psychical 

 accompaniment; both depend not on a generalised ability for judg- 

 ment and appreciating relations, as in intelligent behaviour, but on 

 engrained or enregistered predispositions which are capacities rather 

 than abilities, requiring only the liberating stimulus. 



Instinctive Behaviour of Tailor Ants. — As a useful illustra- 

 tion we take the tailor-ants, which have been often studied since 

 Ridley first described them in 1890. The essential feature is the 

 binding of leaves with silken threads so that a nest is formed 

 which serves for the shelter of the eggs, larvae, and cocoons. 



A first impression is that many grades occur between rough-and- 

 ready structures and astonishing masterpieces; and the obvious 

 lesson is that if the masterpieces alone had survived, the possibility 

 of giving an evolutionary account would have been very remote. 

 It would be a task as hopeless as trying to give an account of the 

 evolution of the human ear, with all its extraordinary intricacy of 

 minute structure, if it were the only surviving ear. When all the 

 many grades of ear are taken into consideration the evolutionist's 

 task is not so hopelessly difficult. Thus in regard to the tailor- ants, 

 Forel tells us that in many cases the silk threads form little more 

 than a tangle binding several leaves together, and providing a simple 

 shelter within which the queen ant lays her eggs and the workers 

 attend to the young ones. It is said that the fruit-growers in the Far 

 East like to have these tailor- ant tangles about their trees, for they 

 believe that the industrious ants capture appreciable numbers of 

 injurious insects. But our present point is merely that the series 

 of nests begins with very simple forms — a long way from the master- 

 pieces. In the common Tailor-ant (Qi^cophjdla), which is widespread 

 in warm countries, what happens is as follows : 



A number of workers combine their forces to draw two leaves 

 together. The margin of one leaf is seized by the mandibles and 

 the margin of the other is gripped by the three pairs of legs. If the 

 gap from one leaf to another is too great to be bridged by one ant, 

 a living chain is formed, somewhat like what we occasionally see 

 among those gymnasts who take our breath away. Ant A grips the 

 leaf with its legs and grips ant B in its jaws, seizing it by the narrow 

 waist. This allows B to grip the other leaf with its jaws. But if B 

 cannot reach the leaf, it takes C in its jaws; and then the chain has 

 three links. We do not know what the maximum number of living 

 links is, but one traveller has told us that he counted six. In any 

 case, even with two or three links, the feat is very remarkable; 

 and as it is not habitual, it may illustrate the intervention of 

 intelligence. 



