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Still more remarkable are the cases in which, as in the Aphis, an egg gives rise to an imperfect female, from which other imperfect females are born viviparously, grow, and in their turns bear other imperfect females; and so on for eight, ten, or more generations, until finally, perfect males and females are viviparously produced.
And some scientist has computed that the aphis, or plant-louse, breeds so rapidly, and in such enormous quantity, that the tenth generation of one set of parents would be so large that it would contain more ponderable animal matter than would the population of China, which is estimated at 500,000,000! And this without counting the progeny preceding the tenth generation!
Presently, the obedient aphis, conscious of its lawful master's friendly presence, begins slowly to emit from two long horn-like tubes near the centre of its back a couple of limpid drops of a sticky pale yellow fluid.
These are all cases of asexual multiplication, and there are other instances, and still more extraordinary ones, in which this process takes place naturally, in a more hidden, a more recondite kind of way. You are all of you familiar with those little green insects, the 'Aphis' or blight, as it is called.
Of course the black golden-rod beetle may try to dwell among the aster flowers, and the aphis that are nursery maids to the ants infest their roots; you must pick off the one and dig sulphur and unslaked lime deeply into the soil to discourage the other, but whatever labour you spend will not be lost.
She feasted thus for four or five minutes, but I am sorry to add that, unlike the humane ants, who care tenderly for their aphides and preserve their lives by kind treatment, the earwig ended by munching up the unfortunate aphis, till not a trace of it was left.
That this law is without exception we are not prepared to say; for in the case of the Aphis certain experiments are thought to imply that under special conditions the descendants of an original individual may continue multiplying for ever, without further fecundation.
Presents always seemed to be flying about in that circle; flowers and boxes of sweets were common currency. My cousins were always getting and giving, my uncle caressed them with parcels and cheques. They kissed him and he exuded sovereigns as a stroked APHIS exudes honey.
A rose-tree, for instance, brought indoors, will soon fall a prey to the aphis, though when hardened out of doors the pest makes next to no impression on it.
The larvæ of insects, whether adapted to the most diverse and active habits, or quite inactive, being fed by their parents or placed in the midst of proper nutriment, yet nearly all pass through a similar worm-like stage of development; but in some few cases, as in that of Aphis, if we look to the admirable drawings by Professor Huxley of the development of this insect, we see no trace of the vermiform stage.
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