MARVEL OF THE APHIS. 



285 



Owen, " should there be this strange combination of vivi- 

 parous generation at one season, and of oviparous genera- 

 tion at another in the same insect ? The viviparous or 

 larviparous generation effects a multiplication of the plant- 

 lice adequate to keep pace with the rapid growth and 

 increase of the vegetable kingdom in the spring and sum- 

 mer. No sooner is the weather mild enough to effect the 

 hatching of the ovum, which may have retained its vitality 

 through the winter, than the larva, without having to wait 

 for the acquisition of its mature and winged form, as in 

 other insects, forthwith begins to produce a brood as hungiy 

 and insatiable and as fertile as itself. The rate of increase 

 may be conceived by the following calculation. The aphis 

 produces each year ten larviparous broods, and one which 

 is oviparous, and each generation averages 100 indivi- 

 duals : — 



have a thirty times greater result."* 



Recovering from the stupor into which we are thrown by 

 facts like these, let us observe that here, as in the case of the 



* Owen : Comparative Anatomy, p. 414. 



