The Perlidæ, or Stone-flies, which, like the Sialidæ, are aquatic Neuroptera, the larval stages being passed in streams, present very puzzling features in regard to the adult males which, so far, have baffled all attempts at solution; yet they seem to have a very important bearing on the all-important work of reproduction. They are among the earliest insects to appear in spring, and possess an extraordinary power of resisting cold. One species, _Capina vernalis_, common in the Albany River, in Canada, frequently comes up through cracks in the ice and casts its skin there! Another, _Nemoura glacialis_, which appears at about the same time, actually performs the nuptial rites in crevices in the dissolving ice! Happily reason is denied them, or they would find life a mockery indeed; for having attained their final development, when the joyous and exhilarating exercise of flight should be theirs, they are compelled forthwith to fulfil their reproductive functions and die—in an ice-chamber! The males have wings which are rarely or never unfurled; as a rule they present nothing more than a crumpled mass of gauzy tissue, as if glued together. Such species as attain to flight are most indifferent performers, travelling but slowly, with laboured movements and settling after a few yards have been traversed. As a rule, among insects, where there is a difference in the power of flight, it is the male which is superior. The case of _Nemoura_, just referred to, affords an instance where the contrary is the case, and Mr. J. J. Lister records the case of one of these flies—_Isogenus nubecula_—taken at Loch Tanna in Arran, wherein the wings of the female were greatly reduced, while those of the male were so much so as to be mere useless vestiges. Similar facts have been recorded of more than one species in Scotland, but in all such cases the phenomenon seems to be associated with the appearance of the insect in very early spring. In another species—_Nemoura trifasciata_—only the front wings are reduced, the hind pair being large enough to cover the body. In male specimens of _Perla maxima_ taken in Scotland, the wings are so short as to be useless for the purposes of flight, yet, in the same species taken in Central Europe, they are of ample proportions. These facts are puzzling indeed, but they seem to show that flight is not essential to attain the ends of reproduction. As to whether these flies secure their mates by any kind of “courtship,” or how they find one another, seems not to be known. But the female is remarkable for the fact that she carries her eggs about with her, to the number of five or six thousand, attached to the end of the abdomen.