The larval or grub phase of life is passed by many of these flies in the earth amidst putrefying vegetable and animal refuse on which they feed, as in the instance of the daddy-long-legs; but here and there we find species which penetrate into the soft parts of plants and animals. A whole group of many species burrow into mushrooms and other fungi when they are grubs; others, again, live in water when they are grubs or "larvæ," and have a very active aquatic life, rising to the surface to breathe air and searching for food in the water with their feelers and eyes, and seizing it with their powerful jaws. The mother fly in these cases lays her eggs in a group on the surface of the water or embedded in a jelly which she secretes and attaches to the leaves of water plants. Some of the short-horned flies (bott-flies and others) lay their eggs in the living flesh of warm-blooded animals, including man, and the maggots hatch there and feed on the juices of the "flyblown" animal. Cases are not rare of children being thus infested. The black flies which fly in swarms "high" or "low" in the country lanes on summer evenings are not true biting gnats, but a large kind of midges known as Chironomus or Harlequin flies. Their eggs are laid in the water of ponds, and the larvæ on hatching bury themselves in the rich black mud and feed there. The larvæ are of a splendid blood-red colour, and are often called "blood-worms." They owe their colour to the presence in their blood of the same red oxygen-seizing crystallizable substance, hæmoglobin, which gives its red colour to the blood of man and other vertebrates. Its presence is remarkable, because in all other insects the blood is colourless or of pale blue or green tint. It seems that this hæmoglobin renders service to the larvæ of the big midges as it does to some other creatures which live in impure water, where free oxygen is very small in quantity, namely, it enables them to absorb and hold by loose chemical combination the small quantity of oxygen available. The minute midges called "Hessian fly" and "Cecidomyia"--injurious to cereal crops--should be mentioned here as among the allies of crane-flies, as also the blood-sucking midges, Ceratopogon, and the minute blood-sucking sand-flies or Buffalo-flies, called "Simulium." Species of Ceratopogon, so minute as to be barely visible, cause terrible annoyance by their bites to the salmon-fisher in Scotland, where they often swarm in countless numbers. The Buffalo-flies attack man, but in some districts of North America alight in thousands on cattle, and cause death in a few hours. A harmless long-horned fly is "the plumed fly," Corethra, the large aquatic larva of which is glass-like and quite transparent, and offers splendid facilities for microscopic research. I used to take it every year in a pond near Hampstead Heath.