622 LIFE : OUTLINES OF GENERAL BIOLOGY 



but they cannot come out again, far less show their fellows the way! 

 Instinct is thus essentially fatalistic. 



Take another case from Fabre's repertory. The mason-bee makes 

 a cylindrical mortar nest, with a lid through which the mature 

 grub bites its way. If the lid is artificially thickened by glueing on 

 a little disc of paper, the grub has no difficulty in cutting through 

 the extra thickness. But if a paper cap be fixed on, like a pill-box 

 inverted, just a little way above the natural lid, but not in contact 

 with it, the grub, emerging into the closed space-between the natural 

 lid, which it has cut through, and the artificial cap, which it could, 

 physically, easily cut through, is nevertheless inhibited fatally. 

 When it has emerged into a free space the cutting instinct ceases 

 and cannot be roused again. The grub dies in its paper prison — for 

 lack of the least glimmer of intelligence to take the place of the 

 satisfied instinct. 



Very interesting ecological observations, at a high level of care- 

 fulness, have been made by Portielje in the Amsterdam Zoological 

 Gardens, Thus he has studied the once common, now sadly dwindling, 

 South American ostrich Rhea; and one of the general facts that he 

 brings out very clearly is the high reach and yet limitedness of 

 instinctive behaviour. When the cock has begun to sit on a few eggs 

 in the shallow depression that serves as a nest, he likes to be visited 

 in natural conditions by members of his harem — in the Amsterdam 

 case, by his one and only wife. She seems half-hypnotised as he 

 stares at her with extraordinary intentness; and she lays an egg 

 close by the nest. Whereupon the brooding cock uses his flightless 

 wings, his bill, and his feathered neck to draw the egg under his 

 body. In a very remarkable way he makes a hook of his neck and 

 adds another treasure to his store. Yet "treasure" is not, strictly 

 speaking, an admissible word, since we know that, before the 

 cock-bird has begun to brood, he passes a dropped egg with non- 

 chalant indifference. A single egg lying anywhere has no meaning 

 for him; in any case, it does not serve to pull the trigger of the 

 incubating instinct. But this impulse asserts itself when he sees an 

 egg, or better still several eggs, in the so-called "nest". Then he 

 begins to brood assiduously, and the eggs — which may eventually 

 number a score — become ncver-too-much-to-be-sat-upon objects. 

 On the one hand, there is high development of an instinct; on the 

 other hand, remarkable limitedness. 



Another instance may be given. When an egg hatches early, 

 before the brooding instinct is waning, the cock rhea is puzzled by 

 the appearance of the nestling. Who is this little stranger? The cock 

 bird, preoccupied with sitting, has no notion of kith and kin, so he 

 sometimes throws his firstborn offspring away! He may do the same 

 with number two. How extraordinarily limited! Yet in a short time, 

 when more nestHngs are hatched out and the incubatory instinct 



