98 LONDON INSECTS 



That is to say, some of the females give birth to living 

 young; others, born usually later in the season, lay 

 eggs. A single egg laid before the cold sets in survives 

 the winter frosts, and the first warm day in spring or 

 early summer an Aphis is hatched, and almost instantly 

 has a family of a hundred females born alive, each of 

 which, without an unnecessary loss of a day, follows her 

 mother's example. The grand-daughters do the same, 

 till ten generations have been born alive. The result, 

 supposing all to live, is 1 x 100 x 100, etc., etc., until in 

 the tenth, not the last generation of the year, the 

 family numbers 1,000,000,000,000,000,000, a quintillion : 

 the figures are Professor Owen's. 1 Then, and this is 

 strangest of all, comes the eleventh generation. When 

 vegetation is rank in spring and summer, the genera- 

 tions of Green-fly, which have to make hay while the 

 sun shines, cannot spare time for such a slow process 

 as being hatched from eggs. That can wait till there 

 is a use for it, and later in the year the use comes. 

 The Aphis is not hardy enough to survive a sharp 

 winter, and so the eleventh generation of the season 

 the whole story sounds too like a fairy tale the 

 eleventh generation is born ' oviparous.' 



When their turn comes to have families, instead of 

 giving birth to living babies they lay eggs, some of 

 which are sure to hatch next spring, and thus save 

 from extinction the race which are the milch cows of 

 the Ants. 



We can see our way more clearly again when we 



1 Invertelrate Anatomy, Lecture XVIII. 



