INTRODUCTION. By L. B. Prout. HI 



and-white or latticed ones like Eulype hastata or C'hiasmia dathrata are, according to experience, very difficult 

 to see, and thus, no doubt, sufficiently escape danger without the aid of a powerful flight, which is possessed by 

 very few indeed of the family. Some gorgeously-coloured exotic genera which certainly fly by day, such as 

 Milionia, Dysphania, etc. are probably more or less distasteful, but we know of no sufficient observations or 

 experiments on this question. The flaunting, crudely-marked ,,Abmxinae" of Japan and Ghma {Obeidia, etc.) 

 are certainly so, and no doubt advertise themselves by their conspicuousness. Concerning Milionia its flight is quite 

 unlike that of an ordinary Geometrid; it shoots away very quickly when disturbed and does not settle at once. 



There are few true Geometridae which enter into mimetic associations. The Dioptidae, which have some- 

 times been placed among Geometridae, are proved both by the larvae and some structural characters in the 

 imago to be entirely distinct from them. The African group of Aletis, however, certainly enters into the Miil- 

 lerian mimetic group of Danaida chrysippus, etc., and there are other scattered instances of the phenomenon 

 in the faunae of New Guinea, tropical America, etc., which will be noticed in their places. 



Owing to the arboreal habits of so many of the larvae — which enable them to be beaten from the bran- 

 ches even when they are too well protected, to render searching profitable — and. to the fact that captured females 

 will as a rule deposit their eggs much more freely than those of many other families, the early stages of a very 

 large proportion of the Palearctic species are already well knoAvn, and even in the other regions a good beginning 

 has been made, although unfortunately m too many cases no descriptions whatever have yet been published. 

 Apart altogether from the biological value of this method of work, breeding is one of the best methods — proba- 

 bly the very best — of obtaining material in this family. So many of the species are fragile and easily rub- 

 bed that it is very difficult to procure captured series in good condition. The eggs are often laid quite readily on 

 the sides of the box in which the $ is confined, but in many cases the insertion of a sprig of the foodplant is 

 a great incentive; in others a preference is shown for very fine rootlets, or shreds of frayed string. 



The larvae for the most part feed on fresh leaves, but the species of Acidalia and some of their allies 

 prefer withered or even mouldy food; one species, Ptychopoda ptelearia, sometimes does considerable mischief 

 in herbalists' shops or in herbaria. As a rule, Geometrid larvae are not at all difficult to rear ; and the frequent 

 wide range of variability of the moths, especially in the temperate and sub-arctic regions, renders them pecu- 

 liarly fitting subjects for various kinds of scientific investigation, whether into the working of the laws of here- 

 dity, the influence of temperature in the production or modification of variation, or the possibilities of hybri- 

 disation between more or less closely allied species. Already in Europe good work has been done in all these 

 directions, and its further pursuit both here and in other parts of the world is highly to be recommended. Men- 

 del's Law of Heredity has been partially tested, with varying results, in Gonodontis hidentata, Abraxas grossu- 

 lariata, Amphidasis betularia, Xanthorhoe ferrugata, Ptychopoda virgularia and others. Mereifield and others 

 have carried out valuable temperature experiments with Selenia, Cosymbia, etc. Hybridisation has also proved 

 in part possible in the two last-named genera and especially among the Biston group. 



As regards the range of imaginal variation it is impossible to summarize it within a limited space. Generally 

 speaking, it reaches its maximum towards the confines of geographical distribution. In Iceland, New Zealand and 

 Chili, for instance, the Geometridae (in common with other families of the Lepidoptera) vary enormously, while in 

 tropical countries it is comparatively exceptional to find a species very variable. The phenomenon of Melanism 

 seems to be there practically non-existent, whereas in some parts of the north of Europe it is exceedingly prevalent. 



Sexual dimorphism is moderately frequent, but seldom reaches any startling manifestation; and much 

 oftener than not, the two sexes are virtually alike in colour and markings, being only distinguishable by structu- 

 ral characters, or by size and perhaps slight differences of shape. The absence of extremes is no doubt due 

 to the general similarity of habits in the sexes and the rarity of true mimicry. Probably the most remarkable 

 examples of this kind of dimorphism are found in the genus Anisozyga, which chiefly inhabits New Guinea and 

 North Australia ; no theory appears to have been as yet offered to explain its occurrence in this genus, and even 

 here it is confined to some only of the species. The South American genus Pero and others and the cosmopolitan 

 Orthonama obstipata (= fluviata) may also be cited as furnishing some moderately striking examples of this 

 phenomenon. Another phase of sexual dimorphism, in which the 9 is apterous or semi-apterous, occurs here 

 and there among the Palearctic and Nearctic Geometridae, in the Australian Zermizinga and one or two South 

 African species referred by Warren to Haggardia. Probably other examples will be discovered amongst species 

 of which hitherto the $ remains unknown; Warren suggests it as likely in the case of his Scoria infumata from 

 Peru. In the majority of instances [Erannis, Alsophila, Operophtera, the Biston group and others) this apterous 

 condition is correlated with the appearance of the moths in the leafless winter season, and various theories 

 have been advanced, with greater or less plausibility, to account for this correlation ; such as that the large wing- 

 expanse necessary to carry the heavy-bodied $ in the stormy winter weather would be a disadvantage to her 

 in the struggle for existence, as rendering her difficult of concealment in the leafless condition of the trees. 



Seasonal dimorphism seems to be strangely rare in the tropics ; yet it is still possible that some sensatio- 

 nal discoveries await us regarding the identity of species hitherto considered distinct, such as have from time 

 to time been made among the butterflies of Africa, for instance, through the careful breeding experiments of 



