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- 

 guished 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, III, 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. ii. d. 



