MPiD il^CEEASE OE iPHIDES. 8l 
It has been very difficult to remove the error, started 
first by Eeaumur, that Aphides in autumn produce 
only modified cocoons, and no true eggs. I quote as 
follows from the article Aphis ’’ in the ‘ Penny Cyclo- 
p83dia,’ written at a period so late as 1834 : — Bonnet 
seems to be of opinion that the Aphides are always 
viviparous, and never lay eggs ; what are commonly 
called eggs, produced in autumn, being a sort of cocoon 
consisting of the young Aphis inclosed in an envelope. 
From our own observation on those of the oak we are 
convinced that this is the fact; but we cannot affirm, 
upon negative evidence, that none of the species lay 
real eggs.’’ It is not easy to guess what the cocoons 
alluded to might have been. Ail the more common 
species of oak Aphis, we now know, lay unmistakeable 
eggs, and we do not doubt that others do likewise. 
In autumn some remarkable oval bodies may be occa- 
sionally seen, which are covered with a striated, 
delicate membrane, which gives them somewhat the 
appearance of a cocoon. These are glued to the leaves 
of the oak, and often found side by side with the 
female Aphis full of her eggs. I have been able to 
watch the hatching of these bodies— for true eggs they 
are, and their produce is not an Aphis, but the larva of 
eacE of wticli again on attaining the age of five days begins the propa- 
gation of 20 young, and completes also that number in twenty days ; 
Then at the end of twenty days from the commencement 
of first Aphis production there would be direct issue . = 20 A. 
At the end of fifth day, progeny A begin to produce, which 
at the end of first twenty days will altogether equal 
15 + 14 -f 13 + 12, &c. + 2 -hi . . . . = 120 B. 
At the end of tenth day, progeny B begin to produce, 
which at the end of the first twenty days will altogether 
equal 10 -f 9 -}- 8, &c. + 2 + 1 . . . . = 55 0. 
At the end of fifteenth day, progeny 0 begin to produce, 
which at the end of the first twenty days will altogether 
equal 5 + 4+ 3 + 2 + 1. . . . .— ISD. 
Total at the end of 20 days equals A + B + O + D .= 210 
The amount, therefore, at the end of 300 days (or 20 x 15) would not 
be less than the fifteenth power of 210, which is almost impossible to 
express in figures. “ There would be room in the world for nothing else 
but Aphides I ” 
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