ZOOGENESIS 



The tunnels and galleries made by many insects in 

 wood or in the ground, which are often very compli- 

 cated, and the tunnels and chimneys made by spiders, 

 the former sometimes provided with a strong hinged 

 lid, show an engineering skill and a knowledge of 

 many of the laws of physics which is really quite 

 remarkable. 



The sometimes enormous nests of termites, the mud 

 and other cells of solitary wasps, and the cells of car- 

 penter, leaf-cutting, Varnisher, and other solitary bees 

 and of wood-boring wasps also may be mentioned as 

 structures which are mechanically and physically per- 

 fect, or at least very nearly perfect. 



Interesting as are these parallels between the activi- 

 ties of man and of the insects, they are perhaps not so 

 surprising as the fact that, except in man, serial fami- 

 lies of helpless and dependent young are found only 

 in certain insects. Successive and overlapping broods 

 of helpless young requiring continuous attention are 

 characteristic of the social ants, bees and wasps and, 

 elsewhere than in man, occur among these insects 

 only. 



The only birds to make use of artificial heat are 

 some of the megapodes or brush-turkeys which are 

 found in the Malayan and Australian regions. These 

 brush-turkeys scratch together a loose mound of 

 leaves, rubbish and earth, lay their eggs in it, and then 

 cover them. The heat arising from the decaying vege- 

 tation in this natural incubator furnishes the warmth 

 necessary for the hatching of the eggs. The same pro- 

 cedure is followed by the alligators and the crocodiles. 



