2l8 DARWINISM AND THE PROBLEMS OF LIFE 



air underneath the water ; this gives it a bright silvery 

 appearance. The water-spider makes underneath the 

 water a diving-bell as large as a wall-nut, bringing 

 down in succession from the surface the air-vesicles it 

 has wound round. It usually lives in these bells, and 

 stores its. prey there. 



If it were said that intelligence prompted the spider 

 to modify its web in this^ way, and practice had made 

 it perfect, the claim would not apply to the bell that 

 the water-spider constructs for its young, which is 

 closed below as well. The spider cannot possibly know 

 that the eggs and the young that issue from them need 

 air. But if the one web has been produced without 

 intelligence and practice, it may very well be the same 

 with the other. 



We are, in fact, compelled to exclude the influence 

 of intelligence in this care of the young by the 

 tracheates, because the parents only make the shelter 

 for them, and never see their offspring, and so cannot 

 know their needs. The black water-beetle spins two 

 plates, lays its eggs inside, and weaves the edges to- 

 gether. It thus forms a raft, one side of which is drawn 

 up in the shape of a little horn, so that it always floats 

 with this uppermost. Still more complicated is the case 

 of the predatory wasps. These powerful creatures fall on 

 an insect, probably a caterpillar, paralyse it by a sting, 

 and drag it into their nests, where they lay the spoil 

 in a cell, deposit an egg on it, and cover up the cell. 

 The larva develops from the ovum, and feeds on the 

 victim, which has been prevented from decaying by 

 being merely paralysed. Sometimes, indeed, the egg 



