302 



SEA-SIDE STUDIES. 



Owen, " should there be this strange combination of 

 \dviparous generation at one season, and of oviparous 

 generation at another in the same insect? The vivi- 

 parous 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 summer. 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 hungry and insatiable 

 and as fertile as itself The rate of increase may be 

 conceived by the following calculation. The aphis pro- 

 duces each year ten larviparous broods, and one which 

 is oviparous, and each generation averages 100 indi- 

 viduals : — 



Gkneration. Produce. 



1st, .... 1 Aphis. 



2nd, .... 100, a hundred. 



3rd, .... 10,000, ten thousand. 



4th, .... 1,000,000, one million. 



5th, .... 100,000,000, hundred millions. 



6th, .... 10,000,000,000, ten billions. 



7th, .... 1,000,000,000,000, one trillion. 



8th, .... 100,000,000,000,000, hundred trillions. 



9th, .... 10,000,000,000,000,000, ten quatrillions. 



10th, .... 1,000,000,000,000,000,000 one quintiUion. 



" If the oviparous generation be added to this, you 

 will have a thirty times greater result."* 



* Owen : Comparative Anatomy, p. 414. [This calculation, however, 

 has been utterly knocked to pieces by HuXLET, in his Memoir on the 

 Aphis, Linncean Trans, xxii. 215.] 



