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It is the pupa, and not the larva, of the Chironomus which has this power; and Grimm further shows that this case, to a certain extent, "unites that of the Cecidomyia with the parthenogenesis of the Coccidae;" the term parthenogenesis implying that the mature females of the Coccidae are capable of producing fertile eggs without the concourse of the male.
The barren Platygaster larva, the fertile Cecidomyia larva, the fertile Aphis larva, the fertile Chironomus pupa, the fertile hydroid polype, and the fertile adult queen bee are simply animals in different degrees of organization, and with reproductive systems differing not in quality, but in the greater or less rapidity of their development as compared with the rest of the body.
Humboldt observed that in some parts of South America each stream had its peculiar mosquitoes, and it yet remains to be seen whether the gnats in Ceylon are also thus restricted in their habitation. The genera Sciara, Cecidomyia, and Simulium, which abound so exceedingly in temperate countries, have each one representative species in the collection made by Mr. Thwaites.
Certain animals belonging to several classes are now known to have the power of ordinary reproduction at an unusually early age; and we have only to accelerate parthenogenetic reproduction by gradual steps to an earlier and earlier age Chironomus showing us an almost exactly intermediate stage, viz., that of the pupa and we can perhaps account for the marvellous case of the Cecidomyia.
The belief in the essential identity of the process of alternate generation and of ordinary metamorphosis has been greatly strengthened by Wagner's discovery of the larva or maggot of a fly, namely the Cecidomyia, producing asexually other larvae, and these others, which finally are developed into mature males and females, propagating their kind in the ordinary manner by eggs.
During the Revolutionary war, the Hessian fly, Cecidomyia destructrix, made its appearance, and it was so called because it was first observed in the year when the Hessian troops were brought over, and was popularly supposed to have been accidentally imported by those unwelcome strangers.
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