1NSECTA. 285 



of iron, in which a narrow and deep groove is cut to receive the plate, 

 which is fixed : the saw of the Tenthredo is also furnished with a 

 back, but the groove is in the plate, and receives a prominent ridge 

 of the back, which is not fixed (to the saw), but permits the saw 

 to slide forward and backward as it is thrown out and retracted. 

 The saw of artificers is single, but that of the Tenthredo is double, 

 and consists of two distinct saws with their backs : the insect, in 

 using them, first throws out one, and while it is returning pushes 

 forward the other ; this alternate motion is continued till the inci- 

 sion is effected, when the two saws, receding from each other, con- 

 duct the egg between them into its place." 



(830.) With respect to the number of eggs laid by insects it 

 varies in different species ; the flea, for example, lays about twelve, 

 and many Diptera and Coleoptera average perhaps fifty : but others 

 are far more prolific ; among moths, for example, the silkworm pro- 

 duces 500, and some from 1000 to 000 : the wasp ( Vespa vulgaris) 

 deposits 3000 ; the ant (Formica), from 4000 to 5000. The 

 queen-bee is said by Burmeister to lay from 5000 to 6000 ; but 

 Kirby and Spence consider that in one season the number may 

 amount to 40,000 or 50,000, or more. Yet, surprising as this 

 latter statement may appear, the fecundity of the queen-bee is far 

 inferior to that of the white-ant (Termes fatalis) ; for the female 

 of this insect extrudes from her enormous matrix innumerable eggs 

 at the rate of sixty in a minute, which gives 3600 in an hour, 

 86,400 in a day, and 2,419,200 in a lunar month : how long the 

 process of oviposition continues in the termite is unknown ; but, if 

 it were prolonged through the entire year, the amazing number of 

 211 ,449,600 eggs would proceed from one individual ; setting, how- 

 ever, the number as low as possible, it will exceed that produced by 

 any known animal in the creation. 



(331.) The Aphides, or plant- lice, furnish a remarkable instance 

 of fecundity. In these insects it has been satisfactorily ascertained 

 by Bonnet, Lyonnet, and Reaumur, that a single sexual intercourse 

 is sufficient to impregnate not only the female parent, but all her 

 progeny down to the ninth generation ! The original insect still 

 continues to lay when the ninth family of her descendants is capa- 

 ble of reproduction ; and Reaumur estimated that even at the fifth 

 generation, a single Aphis might be the great-great-grandmother of 

 5,904,000,000 young ones. 



(332.) Innumerable are the means employed by nature to keep 

 the balance between the increase and destruction of the insect tribes, 



