142 INTRODUCTION 



Vallombrosa plants of Bellis perennis and Anemone nemorosa grew in equal numbers, 

 and were distributed at equal distances from one another. Delpino saw a bee col- 

 lecting pollen from the Anemone with great zeal. When it wished to fly from one 

 plant to another it repeatedly made a mistake and flew to the flowers of Bellis, but 

 having reached these it recognized its error and immediately took wing again. 



In order to reconcile this short-sightedness with the great skill in flight shown 

 by most insects, Notthaft assumes that insects find a standard for judging distance 

 in the varying distinctness of objects, resulting from their different distances 

 the more obscure and confused an object appears to them the further are they 

 removed from it. It may be supposed that insects visiting flowers from considerable 

 distances are guided to a great extent by their sense of smell. By the experiments 

 of Forel, it has been proved, however, that insects certainly perceive flowers at 

 a considerable distance without having recourse to the sense of smell, and that, 

 on the other hand, blinded insects cannot recognize the place where they wish to 

 alight. This investigator cut away the front of the head as far as the eyes, as 

 well as the antennae (with the organs of smell) from some males of Bombus pratorum 

 which were in the habit of visiting a species of Veronica. One of them flew as 

 before from flower to flower, but because it was unable to feed paused only an 

 instant at each and then took wing again. Wasps (Polistes gallica) mutilated 

 in the same way behaved similarly (Kolbe, op. cit., pp. 475, 476). 



The frontal ocelli which many species possess (Fig. 57 a) appear, as their 

 position indicates, to come into action when the insect flies out into the clear sky, 

 or towards a point of light, by enabling the brightness or the source of illumination 

 to be recognized. They are not able, however, to distinguish the forms of 

 external objects. 



Focke (Abh. natur. Ver., Bremen, xi, 1890) summarizes his observations 

 on the visual capacity of flower-visiting insects in the following statements: 



1. Lepidoptera and flies are, in many cases, chiefly guided by the sense of 

 smell to the plants they seek ; in the Hymenoptera, on the other hand, smell serves 

 only exceptionally as an indispensable aid to the discovery of nectar-producing 

 flowers (e. g. in the lime). 



2. Insects can only see very near objects distinctly. At a distance of about 

 ID cm. the visual impressions of bees and humble-bees are indistinct, while some 

 Lepidoptera and flies are still more short-sighted. 



3. Insects receive only confused visual impressions from objects at a greater 

 distance. They are able, however,. to distinguish differences in colour from relatively 

 far off, provided the coloured objects are sufficiently large, and are sharply marked 

 off from their surroundings. A brightly coloured flower, i cm. in diameter, is 

 seen against the greensward by bees, humble-bees, and Lepidoptera, from a distance 

 of I to 2 m. White flowers, when it is dusk, appear to be perceived from much 

 greater distances by hawk-moths. But it remains doubtful whether the insects 

 are not guided by their sense of locality, and by experience acquired during pre- 

 ceding days, to the neighbourhood of the nectar-yielding flowers. 



4. The colour-sense of particular species of insects is developed to varying 

 extents and in different ways. 



