388 PSYCHOLOGY. 



tuous thrill may not shake a fly, when she at last discovers 

 the one particular leaf, or carrion, or bit of dung, that out 

 of all the world can stimulate her ovipositor to its dis- 

 charge ? Does not the discharge then seem to her the only 

 fitting thing ? And need she care or know anything about 

 the future maggot and its food ? 



Since the egg-laying instincts are simple examples to con- 

 sider, a few quotations about them from Schneider may be 

 serviceable : 



" The phenomenon so often talked about, so variously interpreted, 

 so surrounded with mystification, that an insect should always lay her 

 eggs in a spot appropriate to the nourishment of her young, is no more 

 marvellous than the phenomenon that every animal pairs with a mate 

 capable of bearing posterity, or feeds on materials capable of affording 

 him nourishment. . . . Not only the choice of a place for laying the 

 eggs, but all the various acts for depositing and protecting them, are 

 occasioned by the perception of the proper object, and the relation of 

 this perception to the various stages of maternal impulse. When the 

 burying beetle perceives a carrion, she is not only impelled to approach 

 it and lodge her eggs in it, but also to go through the movements re- 

 quisite for burying it; just as a bird who sees his hen-bird is impelled 

 to caress her, to strut around her, dance before her, or in some other 

 way to woo her; just as a tiger, when he sees an antelope, is impelled 

 to stalk it, to pounce upon it, and to strangle it. When the tailor-bee 

 cuts out pieces of rose-leaf, bends them, carries them into a caterpillar- 

 or mouse-hole in trees or in the earth, covers their seams again with 

 other pieces, and so makes a thimble-shaped case — when she fills this 

 with honey and lays an egg in it, all these various appropriate expres- 

 sions of her will are to be explained by supposing that at the time when 

 the eggs are ripe within her, the appearance of a suitable caterpillar- or 

 mouse-hole and the perception of rose-leaves are so correlated in the 

 insect with the several impulses in question, that the performances fol- 

 low as a matter of course when the perceptions take place. . . . 



" The perception of the empty nest, or of a single egg, seems in birds 

 to stand in such a close relation to the physiological functions of ovipa- 

 ration, that it serves as a direct stimulus to these functions, while the 

 perception of a sufficient number of eggs has just the opposite effect. 

 It is well kuown that hens and ducks lay more eggs if we keep remov- 

 ing them than if we leave them in the nest. The impulse to sit arises, 

 as a rule, when a bird sees a certain number of eggs in her nest. If 

 this number is not yet to be seen there, the ducks continue to lay, 

 although they perhaps have laid twice as many eggs as they are accus- 

 tomed to sit upon. . . . That sitting, also, is independent of any idea of 

 purpose and is a pure perception-impulse is evident, among other things, 



