Proceedings of the fourth International Congress of Zoology, Cambridge, 22-27 August, 1898 / edited by Adam Sedgwick.

Date:
1899
Catalogue details

Licence: Public Domain Mark

Credit: Proceedings of the fourth International Congress of Zoology, Cambridge, 22-27 August, 1898 / edited by Adam Sedgwick. Source: Wellcome Collection.

Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.

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    3. Some points in the classification of Insecta Hexapoda. By Dr D. Sharp. Although there is a generally accepted opinion amongst zoologists to the effect that the branch of ontogeny called meta- morphosis is of great importance in the study and classification of Insects, yet it is certain that the efforts that have been made to utilise the known facts are far from final. The terms Ametabola, Hemimetabola, etc. that have been used are not sufficiently definite for taxonomic purposes, or for a lucid consideration of the subject. One point of considerable importance has escaped attention, and this point I think will be found to furnish us with an additional, definite criterion as to the metamorphosis of insects. It is that in one set of cases the wings are developed outside the body, while in another set of cases they are developed inside the body and become suddenly external. The number of insects that can be correctly said to be entirely destitute of the phenomena of metamorphosis is very small indeed. As all of us know they are called Ametabola. For those that exhibit the phenomenon of metamorphosis Packard has recently proposed to adopt four categories, viz. Manometabola, Here- metabola, Hemimetabola, Holometabola ; these terms, in addition to that of Ametabola and to that of the condition of acquired ametabolism (indicated by Lang but apparently as yet without name), make no less than six categories of metamorphosis ; and in addition to them we meet with other terms, such as Paurometabola. These terms indicate the amount of metamorphosis. But they do so in only a very vague manner, and I think we shall gain by considering them as of subordinate importance to the nature of the wing development. On the accompanying table the names of the great divisions of existing insects that have not been satisfactorily connected by morphological and ontogenetic study are placed in a consecutive arrangement, and are grouped in accordance with our present knowledge under four heads, Apterygota, Anapterygota, Exoptery- gota, Endopterygota : these four groups represent generalisations as regards the development of the wings. The Apterygota include the two orders Thysanura and CoUem- bola. These insects are quite wingless, and are usually considered to be the descendants of a stock never having possessed wings. The Apterygota exhibit, so far as is known, but little or no metamorphosis during the postembryonic period. The Anapterygota consist of wingless forms that are supposed to be descended from winged forms. They are all parasitic on vertebrates during the whole or part of their lives. The evidence