PACKAKDl INSECTS OF THE GARDEN. 35 



have made out microscopically, are probably all or nearly all 

 fecundated. We have, then, for every two individuals which 

 have appeared this year, a deposit of five hundred embryos 

 for the generation to appear seventeen j-cars hence. 



Now, from what has just been stated about the uniformity 

 of their numbers, each time, it apix'ars that from the liabili- 

 ties of destruction during the long term of seventeen years, 

 out of these five hundred embryos, only two appear certain 

 of life and appearance iu their perfect state, that is, just re- 

 placing the two parents. The chances of life therefore with 

 this iusect, are, in round numbers, two in five hundred. This 

 calculation may seem strange to some, but if we reflect, it 

 can scarcely be otherwise ; for suppose the chances were 

 double, that is, four in five hundred, then we should have at 

 each time just double the numbers of their last time, which 

 observation has shown to be untrue and which would augur 

 much evil for the future condition of the vegetable world in 

 the localities of their appearance. Even if their chances 

 were three in five hundred, or half again the original stock, 

 agriculturists would quickly perceive the difference. 



To sum up the matter, then, we have here an insect whose 

 economy and conditions of life are so unique that it is almost 

 entirely isolated from human destructive agencies and which 

 is obliged to deposit five hundred chances for the certainty 

 of securing two. The ovaries have been formed with this 

 capacity and the whole internal economy is of a correspond- 

 ing character." 



The sluill noise made by the male Cicada, "for," says 

 Anacreon, "they all have voiceless wives," originates in two 

 kettle-drum-like organs situated under the wings at the base 

 of the hind body. 



The Aphis (Fig. 24). — We should not be doing justice to 

 the subject of garden pests if we omitted a special notice of 

 that Avonderful creature, the Aphis or I'lant Louse. Tl e 

 first to appear in spring as the buds unfold, the very last to 



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