136 THE ENTOMOLOGIST. 
Diptera I have found at present almost confined to the 
Syrphide. In my own little garden, and in the gardens of 
the Royal Botanic Society, in the Regent’s Park, I have been 
in the habit, during the last few summers, of capturing 
specimens of the two most common species, Eristalis tenax 
aud Syrphus clypeata, eviscerating them, and examining the 
contents of the abdomen under the microscope, which I 
found to be coloured a bright orange, by the presence of 
enormous quantities of the peculiar spined pollen-grains 
characteristic of Composite, and evidently obtained from the 
various species of Aster, over which such numbers may be 
seen hovering. ‘That they are not accidentally taken up, but 
form an actual article of food for the flies, is sufficiently 
proved by finding them in every stage of digestion, the fluid 
contents of the pollen-grains being apparently the nutritive 
substance, and the skins being ultimately excreted. Speci- 
mens of several species of Muscide, captured on the flowers 
of the Aster, when examined in the same manner furnished 
only a very few grains of pollen, apparently sucked up acci- 
dentally through the proboscis with the fluid food. During the 
present spring I captured, on the flowers of the sloe, Eristalis 
tenax and Andrena fulvicrus (male and female). The abdo- 
men of the former was full of pollen-grains, belonging to at 
least three kinds of plants,—the sloe, the dandelion, and 
some large triangular pollen-grains, apparently those of 
Fuchsia. The tubes of the latter species contained only a 
very few grains, as was also the case with the honey-bee, the 
pollen belonging in the latter case apparently to the dande- 
lion. I was interested at the same time in watching the 
constancy with which insects visit only the same species of 
flowers on the same visit. In the case of a bank covered with 
the white dead-nettle, red dead-nettle, and ground-ivy, the 
white dead-nettle was visited only by one species of humble- 
bee, Bombus Pratorum and Anthophora retusa; the ground- 
ivy only by the hive-bee, except on two solitary occasions by 
the Anthophora; while the red dead-nettle was entirely 
neglected by both, the only insect observed to visit it being 
~ a butterfly, Vanessa Urtice. An examination of the pollen 
carried away on the thighs of the hive- and humble-bees con- 
firmed this observation, the pollen-grains of the three species 
named being particularly easy to distinguish by their colour: 
