40 THE DARWINIAN THEORY 



second generation we shall have 64 millions of 

 millions of female oysters. In the fifth generation— 

 i.e., the great-great-grandchildren of our first oyster— 

 we should have 33 thousand millions of millions of 

 millions of millions of millions of female oysters. 

 If we add the same number of males we should have 

 in all 66 + 33 noughts. If we estimate these as 

 oyster-shells, we should have a mass more than eight 

 times the size of the world. 



A large number of eggs or young is, however, not 

 essential. The Fulmar petrel lays only one egg, yet 

 it is believed by Darwin to be one of the most 

 numerous birds in existence. The Passenger pigeon 

 again only lays two eggs, yet it is extraordinarily 

 abundant in parts of North America, where its enor- 

 mous migrating flocks darken the air for hours. A 

 remarkable account is quoted by Wallace of a wood 

 in Kentucky, 40 miles in extent, where there was a 

 perpetual tumult of crowding and fluttering pigeons, 

 and where there were as many as a hundred nests 

 on a single tree, the branches of which were often 

 broken off by their weight, and the ground strewn 

 with broken limbs of trees, eggs, and young birds, on 

 which herds of hogs were fattening. Hawks, buz- 

 zards, and eagles were flying about in large numbers, 

 seizing the young birds at pleasure ; and numerous 

 parties of men from all parts of the adjacent country 

 were camping with their families for several days, 

 felling trees to get the nests. 



Another good example of rapid increase in num- 

 bers was seen in the rabbit pest of Australia in 

 1887. The common grey variety of wild rabbit 



