As soon as they are brought into the world, they insert their suckers, absorb a little sap, increase in size, and in a few days become capable of continuing the race by the same rapid method, without fathers. Until the end of the annual colonization the offspring, including the remotest degrees of descent, will maintain the process of genesis by direct parturition and will know no other method. When the time has come for a more convenient examination, we shall return to this amazing method, which completely upsets our ideas.
On the 1st of May I open some of the purple swellings which have formed on the tips of the burgeoning leaflets. Sometimes I find the maker of the capsule alone, just as she was on the tips of the buds; sometimes [[252]]she has undergone a moult and is accompanied by the beginnings of a family. After discarding her black slough, she has become greenish, corpulent and lightly dusted with flour. Her youngsters, at the moment one or at most two, are brown, slender and bare-skinned.
In order to follow the progress of the family, I place under a glass a couple of capsules which so far contain only the founder. Two days later I have a dozen young Lice, who soon desert the natal pocket and make for the cotton-wool closing the glass tube. This hasty migration indicates that the young Lice have their function elsewhere, on the tender, already unfolded leaves. Detached from its fostering support, the little purple cell dries up and its inhabitant dies. My census can no longer be continued. No matter: I have learnt that one day is enough to produce three births. If this birth-rate persists for a fortnight, the maker of the capsule will have brought forth a handsome family, gradually scattered over the wide field of exploitation offered by the terebinth.
A fortnight later the red eggs hatch out, when the young twigs are already shooting [[253]]and unfolding their leaves. As far as I could judge from my highly unreliable observations of these swarming insects, which are not clearly distinguishable one from the other, the later generation begins as did the earlier. It causes purple nodules to appear on the tips of the leaflets, little wallets similar in shape and size to a grape-stone. Like those already mentioned, these cells are inhabited at first by a single Plant-louse.
In both cases the rage for rapid multiplication is the same. The recluses soon produce offspring, who desert the natal shelter and proceed to settle elsewhere as colonists. At last, its flanks drained dry, the viviparous little insect dies in its withered arbour.
How many were they, coming from under the lichens and climbing to the assault of the terebinth? There were thousands of them; and this multitude is not enough. Hastily each Louse attacks her leaflet with her beak; she makes herself a lair out of its swollen tip and immediately gives birth to other Lice, multiplying ten- or perhaps a hundredfold in this invasion of the innumerable. The tree has now its full number of colonists, [[254]]all capable of founding populous tribes.
Are we to regard them as different branches of the same trade union, of the same family, exploiting the terebinth in various fashions, according to the point attacked? We hesitate to regard them as strangers to one another, when they are employed on the same work; yet there are significant reasons for concluding that we have here a duality or multiplicity of species.
Besides the disparity of the work accomplished, there is, at the outset, one distinctive feature: the colour of the eggs, of which some are black and others red. These vividly contrasted hues must correspond with independent ancestries. It is even possible that a patient examination, capable of analysing this minute object, would find differences in husks of the same colour. All my own searches beneath patches of lichen and in the crevices of dead wood end in nothing more than the discovery of two sorts of ovular carapaces but of two only, at least to judge by appearances; and yet on the tree we shall find five categories of workers who, though resembling one another, build very dissimilar structures. If there are no other [[255]]germs, germs which have escaped my careful observation, it would seem, therefore that the eggs have different contents under an identical shell, whether black or red.
Lastly, the configuration, that essential characteristic of the species, displays, in late autumn, very emphatic differentiating features. Up to this late season, the inmates of the galls of every form are so much alike that it is impossible to distinguish them one from another once they are taken from their dwellings. When the final exodus comes, at the close of the year, a generation makes its appearance which differs greatly from its predecessors, giving final proof of multiple species, to the number of five.
Their generic name is Pemphigus, which is to say, bubble, capsule, bladder. This scientific name is well deserved. The Terebinth-lice and some others that pursue similar callings, living on the elm and the poplar, are, in a word, artificers of swellings: by the incessant tickling of their suckers they cause the formation of hollow excrescences, which are at once board and lodging to the community.