Page:The Zoologist, 3rd series, vol 1 (1877).djvu/297

Rh that the converse will be found to hold good, viz. that should the completion of the pupal stage be retarded either by cold seasons or climates in a state of nature, or artificially by aid of an ice-well, illustraria, not delunaria, would be found to result from illustraria.' And again (loc. cit. p. 256) he puts it thus:—'If I. = illustraria, D. = delunaria, and—= winter; then if there be but one brood in the year the sequence will be I.—I.—I., and so on; if two broods, I.D.—I.D.—I.D., and so on; if three broods, I.D.D.—I.D.D., and so on.'

"I have not yet tried the effect of artificial retardation on the pupæ of Ephyra, but intend to do so when opportunity offers. My experiment shows that the effect of natural retardation over the winter months is to produce the type whatever may be the form of the parents; and that such natural retardation does usually (? always) occur in polygoneutic species I believe to be true from my experience in breeding various insects. Remembering that the summer broods of season-dimorphic species are smaller, and apparently vitally weaker than the spring ones, and that it is from the former that the latter are usually descended, may we not assume that the provision by which some few of the direct offspring of the spring forms are preserved through the winter in the pupal state, and so are enabled to pair with the offspring of the summer form, is of advantage to the species, in affording a 'cross' between individuals which have developed under very different conditions? A similar benefit may be derived in the commonly observed case of individual pupæ of single-brooded moths (e.g. Eriogaster and many Notodontidæ) remaining two, three, or more years in that stage, and then eventually making their appearance at the proper season with the ordinary flight of the species.

"As bearing on the above suggestion, I may refer to what occurs in those single-brooded moths (Sphinx Convolvuli, Acherontia Atropos, &c.), which sometimes appear abnormally from the pupa before the winter hybernation, or which by 'forcing' have been artificially so developed. It has been stated, I believe, in most such cases in which an anatomical examination has been made, that the ovaries, &c., were found in an abortive or rudimentary condition. This goes to show that a long period of quiescence is necessary to perfect these delicate and highly specialized organs, and by a parity of reasoning it may perhaps be assumed that those pupæ which remain longest in that stage will (ceteris paribus) produce the most highly developed and vitalized images."

The President read "Notes upon a Strepsipterous Insect parasitic on an Exotic Species of Homoptera (Epora subtilis, Walk.) from Sarawak," accompanied by drawings illustrating the metamorphosis. He also read Notes on the Genus Prosopistoma, especially with regard to the species from Madagascar described by Latreille, of which he exhibited the types.