In the centre is seen a group of eggs of the Lace-wing Fly (Hemerobius), so called on account of the delicate, lace-like structure of its beautiful pale green wings.
When the female lays her eggs she always chooses a slight twig, and upon it deposits a little drop of a slimy consistence. She then draws out this drop into a thread, which hardens as it is brought into contact with the air. At the extreme end of the thread she places an egg, which is thus kept at some height above the ground, and defies the approach of inimical insects. The eggs, as well as the stalks, are perfectly white, and have so singular a resemblance to mosses, that for many years they were actually classed and figured as such.
These egg-groups are plentiful enough, if the observer only knows where to look for them. I have several of them in my collection, and have found that nearly every one who sees them for the first time takes them for mosses. I never myself saw the pretty insect lay its eggs, and for the description am indebted to Mr. A. G. Butler, of the British Museum, who has kept them and watched their habits.
The objects on either side of the Lace-wing Fly’s eggs are egg-groups of certain spiders, suspended by threads from branches.
A still more remarkable instance of unconscious imitation may be found in the two objects in the accompanying illustration. It is hardly necessary to say that the right-hand figure represents a portion of the arrangement by which a butcher hangs up his meat out of harm’s way until it is wanted.
The hooks in question are simply formed into a double curve, like the letter S, and can be slid along the horizontal bar without any danger of falling.
Now, in the common Sloth we have an exact prototype of the butcher’s hook. The Sloth passes the whole of its life in the remarkable attitude which is shown in the illustration. It lives among the branches—not on them, but under them—its claws being long and curved, just like a butcher’s hook. I have often watched the animal traversing the branches, and have been greatly struck with the accurately picturesque description of the late Mr. Waterton, who was the first to discover the real character of the Sloth.
It was he who found out that the previous ideas as to the Sloth’s mode of life were utterly erroneous, and that, instead of being a sort of bungle, the Sloth was as perfect in its way, and as well fitted for its mode of life, as the lion or tiger. He discovered that the animal always hung from the branches, as shown in the illustration. In fact, as Sydney Smith remarked in his witty review of “Waterton’s Wanderings,” the Sloth passes his whole life in suspense, “like a young clergyman distantly related to a bishop.”
There are many other creatures which afford similar examples, though perhaps none are so striking as the Sloth.