Packard] INSECTS OF THE PLANT HOUSE. 105 



a mammary gland," and he then compares these insects in 

 this respect to the mammals. 



Now upon pressing the body of the Aphis, placed in a 

 drop of water in the animalcule stage, we readily squeeze out 

 the contents of the abdomen, including the ovaries. Instead 

 of a numerous mass of eggs in various degrees of maturit}', 

 we are astonished to see a series of young Aphides, in va- 

 rious stages of development. The creature brings forth its 

 young alive. Moreover, the parent, as Bonnet observed, is 

 a virgin. No males are in existence. The first brood hatch- 

 ing out in the spring are all females. As soon as the leaves 

 unfold the virgin rears its brood of young ; these in turn 

 produce their spinster offspring, and the number of broods is 

 only limited by the approach of frost. Finall}', after from 

 eight to ten broods, males and females appear ; the latter lay 

 fertilized eggs, by which the species is represented during 

 the winter. Such are the powers of multiplication of these 

 Aphides that a s[)ring-born virgin ma}^ become tlie happy 

 mother of a (luintillion daughters and granddaughters. At 

 least such is the belief of M. Fougard as quoted by Prof. 

 Morren in his well known paper "Sur le Puceron du Pecher." 

 A certain species which Fougard calls " Puceron lanigere" 

 produces ten viviparous generations and one oviparous gen- 

 eration. PLach generation produces from ninety to one hun- 

 dred and fifteen individuals, the mean of which is one 

 hundred. He thus obtains the following table of genera- 

 tions : — 



l-t 1. Aphis, 



'2il 100, o:io Imnilrcd. 



;M 10,000, tLMi Ui(ius;inil. 



4th 1,000.000, one ni;li;ou. 



5th lOO.OCO.dOO, liuiulred millions. 



Cth 10,0..0,(;00 000, ten billions. 



7th l,(;o 1,00.1,000,(00, one trillion. 



8th .... 10.),0;)0,000.0;.0 0.)0, hundicil ti-il'ions. 



nth . . . 10.00 ),0(;0,( 00,0)0,(00, tin (luaihilli.ins. 



lOlh . . . l,C00,0.i0,C0J,0C0,0J0,000, ouo iiuintillioii. 



9 



