192 INTRODUCTION 
Stage I. Hemiptera, Neuroptera, Panorpidae, Trichoptera, Dermaptera, and 
part of the Coleoptera. The mouth-parts and hairy covering do not show any 
distinct adaptations to flowers: the activity of the visits is very slight and their 
number very small. 
Stage II. Many Coleoptera, Diptera, Orthorrhapha (except Empidae and 
Bombyliidae), Muscidae acalyptratae; Phytophaga, Entomophaga, and Formicidae 
among Hymenoptera. Here again distinct adaptations of mouth-parts and hairy: 
covering are wanting, but visits are more numerous and their activity is markedly 
greater. 
Stage III. Fossores, Chrysididae, and Diploptera among Hymenoptera ; 
Empidae, Bombyliidae, Syrphidae, Conopidae, and Muscidae calyptratae among 
Diptera ; also a few Coleoptera. The mouth-parts or hairy covering show more or 
less distinct adaptation to the flowers sought out by these insects. All are regular 
flower visitors. 
Stage IV. Short-tongued Anthophila (bees with unspecialized labial palps). 
Not only are the mouth-parts—and usually the hairy covering as well—thoroughly 
adapted to flowers, but adults as well as larvae are dependent on flowers to such an 
extent that they could not live without them. They are not only regular, but also 
very energetic agents of pollination. 
Stage V. Long-tongued Anthophila (bees with specialized labial palps). The 
mouth-parts are greatly elongated and the hairy covering usually very well developed. 
These insects are larger as a rule than bees with unspecialized labial palps. Owing 
to various improvements of the collecting-apparatus, their visits are made more 
rapidly, being at the same time more productive for themselves, and more beneficial 
to the flowers. The number and activity of visits reach a maximum. Adults and 
larvae are necessarily entirely dependent upon flowers. 
Stage VI. Lepidoptera. Those which are regular flower visitors are distin- 
euished by the possession of a more or less conspicuously long proboscis that can 
be rolled up. The adults are dependent upon flowers so far as they partake of 
nourishment of any kind. Since they take no care of their offspring their activity in 
visiting flowers is much less than that of the two preceding stages, and they have 
about the same value for pollination as Stage III. They are very important for 
flowers with long and narrow tubes, to which the proportions of their proboscis 
correspond. This organ must have become highly specialized at an early period of 
the earth’s history, for transitional forms between Lepidoptera and their relatives the 
Trichoptera do not now exist. 
The value as regards pollination of Verhoeff’s six stages of adaptation is as 
follows:—I, II, IIJ, VI, IV, V. This classification into stages is undoubtedly of 
great value, and in many ways agrees very closely with the actual facts. Yet it is to 
be remarked that the ‘regular flower visitors’ of Stage VI, including the hawk-moths 
‘(Sphingidae), are at a much higher level as regards adaptation to flower pollination 
than Verhoeff supposes. 
The classification of insects that visit flowers given by E. Loew appears to me 
to correspond more accurately with nature than that of Verhoeff (‘Beob. ui. d. 
