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@) 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 
1o 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, 1 cm. in diameter, is 
seen against the greensward by bees, humble-bees, and Lepidoptera, from a distance 
of 1 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. 
