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the material it is employing for its building. This is turned on every side, either in order to discover whether the piece will or will not suit, or else to find out which is the side that will best fit into the space required for it. If the piece is found to answer all the purposes required by the caddis, it is cemented into the space reserved for it by this secretion, which proceeds from its mouth. If, however, the piece. does not suit the space, that piece is instantly rejected, and another one is taken up by the worm in the same manner as the previous one was. Sometimes the caddis is obliged to take up several pieces before it is able to meet with one fit for the purpose. This makes the task of building extremely tedious and laborious. Indeed, with the creature's slender legs it seems marvellous that it is able to take up the different pieces with them, particularly when heavy ones are selected, which is the case when the worms inhabit rough waters; for in those localities the materials are principally large stones, or else thick heavy bits of wood, which must render the building extremely laborious. The building is continued by the caddis, in the manner just described, without stopping, until it has succeeded in raising a house according to its taste. When it has completely finished, the whole body of the worm is encased in it with the exception only of its head and legs, and even these are capable of being drawn into its building, either for its pleasure or for their protection at the appearance of danger.'
As to the time taken for a caddis to build its case, there is great difference amongst individuals. Some take much longer time than others, and require a week or more to do what another will perform in twenty-four hours. When the larva is about to assume its proper form, it spins a grating over the entrance of the case, and remains dormant till it assumes the condition of a perfect insect.
We will now draw attention to one of the most wonderful of all house-building creatures, when we consider that the architect is a minute worm, scarcely visible to the naked eye of any but a naturalist, a little delicate thing about as thick as a horsehair, and the twelfth part of an inch in length. The little creature in question, which is known by the name of Melicerta ringens, is common enough in clear ponds, where it may be found sometimes in extraordinary profusion attached to the leaves or stems of various aquatic plants. How is it that Mr. Wood, who has evidently used his eyes to some purpose, has omitted all notice of this exquisite little creature as a builder? In the whole aquatic world of animals there is surely no more interesting object for contemplation than the Melicerta. As we have frequently witnessed the manner in which this little creature builds its own house, we will endeavour to explain it to the reader. But, first, as to the places where it is found. As we
*See Intellectual Observer,' vol. v. p. 307.
have said, in almost all clear water, such as mill-pools and ponds, through which a current of water gently flows, the melicerta may be found. If a portion of water-weed be brought home and placed in a glass vessel, and the leaves of the plants be carefully examined with a lens, the observer will probably detect delicate projecting objects of a reddish colour, light or dark, according to the nature of the bottom of the pool. These are the tubular cases of the melicerta. If one of these be placed on a slip of glass and viewed under the microscope with a power of about fifty diameters, we shall notice that this tube is made of several series of round clay or mud pellets. By-and-by, if we do not shake the table on which our specimen is placed (for melicerta is a timid creature), we shall see the occupant slowly unfold the anterior portion of his body from the orifice of the tube. At first, as has been well described, 'a complicated mass of transparent flesh appears involved in many folds, displaying at one side a pair of hooked spines, and at the other two slender truncate processes projecting horizontally. As it composes itself more and more, suddenly two large rounded discs are expanded, around which, at the same time, a wreath of cilia is seen performing its surprising motions. Often the animal contents itself with this degree of exposure, but sometimes it protrudes further, and displays two other smaller leaflets opposite to the former, but in the same place, margined with cilia in like manner. The appearance is now not unlike that of a flower of four unequal petals; from which resemblance Linnæus, who compared it to a ringent labiate corolla, gave it the trivial name of ringens, by which it is still known.'* By continuing to gaze on this marvel of creative skill, we notice that it every now and then bends its corolla-shaped head down upon the tube, holding it there a second or two, and then raising it up again. What is the meaning of this? Melicerta is adding a brick to his house; sometimes the bricks fall off after deposition, the material used not being sufficiently tenacious. The bricks are made of the same substance which human architects so generally use, namely, of clay, the only difference being that the bricks of the rotifer are round and soft. Under a power of about 200 diameters the observer will see a singular circular cavity below the large discs of the head; this cavity gradually becomes filled with particles of clay; a number of cilia line the cavity, and by their action cause the particles of clay to rotate rapidly, and to be consolidated. When the brick is formed the animal bends down his head and affixes
* See Gosse's "Tenby,''p. 313, and Plate xxi., where there is an admirable drawing of this creature.
it to the tube, and then begins to form another pellet. The particles of clay or other adhesive material are drawn into the cavity where the bricks are formed by the ciliary action of the discs, a small channel conducting them from the upper portion of the disc to the cavity in question. If portions of carmine or indigo be mixed with the water in which the melicerta lies, the animal will make use of them and add rings of red or blue to its tube. It is impossible to imagine a more interesting instance of animal architecture than that exhibited by this minim of creation.
The marine worms, known as Serpulæ, Sabellæ, and Terebellæ, so common on every coast, construct their own cities of stones, shells, mud, sand, &c., in which they dwell. This they do by means of their tentacles, which they use as fingers, grasping particles of sand and mud, and adding them to their tubes. Mr. Gosse has given an interesting account of the mode in which the Sabella vesiculosa builds its house of mud.
That extremely beautiful bivalve mollusc, the lima, constructs for itself a habitation, in which it lives, not by boring into stone or wood, as in the case of the pholas already mentioned, but by binding together bits of coral, nullipore, &c., with its byssus filaments.
'It is not contented with hiding itself among the loose coral, for the first rude wave might lay it naked and bare; it becomes a marine mason, and builds a house or nest. It chooses to dwell in a coralgrotto; but in constructing this grotto it shows that it is not only a mason, but a rope-spinner, and a tapestry-weaver, and a plasterer. Were it only a mason it would be no easy matter to cause the polymorphous coral to cohere. Cordage then is necessary to bind together the angular fragments, and this cordage it spins, but how it spins it is one of the secrets of the deep. By some means or another, though it has no hand, it contrives to intertwine this yarn among the numerous bits of coral so as firmly to bind a handful of them together. Externally this habitation is rough, and therefore better fitted to elude or to ward off enemies; but though rough externally, within all is smooth and lubricous, for the fine yarn is woven into a lining of tapestry, and the interstices are filled up with fine slime, so that it is smooth as plasterwork.'*
This 'nest'-making habit is not restricted to full-grown individuals; the nests are generally found under large stones at lowwater mark; sometimes several are contained in one habitation. Lima hians is abundant at Herm, and the people of the island call these shells, 'angel's wings.' Properly speaking, the lima grotto is no nest in the sense in which we speak of a bird's-nest,
* Rev. David Landsborough in Rymer Jones's 'Aquarian Naturalist,' p. 475,
for it is not constructed for the temporary purpose of rearing and concealing the young, but for the permanent abode of individuals of all ages.
Of mammalia that build social habitations the beaver is the most conspicuous; and, although many exaggerated accounts have been written of the operations of these animals, the fact remains that they are most skilful engineers. Mr. Wood describes the manner in which the beaver forms a dam.
'When the animal has fixed upon a tree which it believes to be suitable for its purpose, it begins by sitting upright, and with its chisel-like teeth cutting a bold groove completely round the trunk. It then widens the groove, and always makes it wide in exact proportion to its depth, so that when the tree is nearly cut through it looks something like the contracted portion of an hour-glass. When this stage has been reached, the beaver looks anxiously at the tree, and views it on every side, as if desirous of measuring the direction in which it is to fall. Having settled this question, it goes to the opposite side of the tree, and with two or three powerful bites cuts away the wood so that the tree becomes overbalanced, and falls to the ground. This point having been reached, the animal proceeds to cut up the fallen trunk into lengths, usually a yard or so in length, employing a similar method of severing the wood. In consequence of this mode of gnawing the timber, both ends of the logs are rounded and rather pointed.'
The next part of the task is to make these logs into a dam, so as to keep the water to the proper level. The logs are placed horizontally, and formed into a mass with earth and stones, so as to be sufficiently strong to resist the force of the stream. Instances of dams measuring two or three hundred yards in length, and ten or twelve feet in thickness are not uncommon. It is curious to observe that if the water rises with a strong current the dam is made in a convex shape, so as the better to resist the force of the water; but if the stream runs slowly, the dam is carried straight across the river.
'In places,' says Hearne, who has given an excellent account of the habits of this animal, which have been long frequented by beavers undisturbed, their dams, by frequent repairing, become a solid bank, capable of resisting a great force, both of water and ice; and as the willow, poplar, and birch generally take root and shoot up, they by degrees form a kind of regular planted hedge, which I have seen in some places so tall that birds have built their nests among the branches.'
The dome-shaped beaver-houses are built of the same materials as the dams, being proportioned in size to the number of inhabitants, there being generally four old ones, and six or seven young
Sometimes there are several divisions or apartments in a beaver-house, but they are not, as a rule, connected with each other except by water. Hearne says he once saw a large beaverhouse built in a small island that had near a dozen apartments under one roof, but with two or three exceptions, they had not communication with each other except by water. As there were beavers enough to inhabit each apartment, it is more than probable that each family knew their own, and always entered at their own doors, without any further connection with their neighbours than a friendly intercourse, or to join their united labours in erecting their separate habitations, and to help in adding to the dam when requisite.
The old story about the beaver using its broad flat tail as a trowel to smooth over the mud of its house, it is hardly necessary to add is a fiction. When it originated we are unable to say; the ancient natural history writers, Aristotle and Pliny, do not allude to it. The error no doubt arose from the habit of the animal constantly slapping its tail as it moves along.
In his chapters on Social Insects, Mr. Wood gives us, amongst other interesting matter, an account of one of the most terrible insects in existence; this is the Driver Ant (Anomma arcens) of Western Africa. Like many species of ants, this insect is remarkable for its sagacity and skill. We shall conclude our sketch of the architecture of animals with a notice of the habits of this insect. It is a curious fact that though found in immense numbers, it has never yet been discovered in the winged condition, and the male and female are unknown.
'The workers are uniform in colour, but exceedingly variable in size. Their hue is deep brownish black, and their length varies from half an inch to one line, so that the largest workers nearly equal the common earwig, while the smallest are no larger than the familiar red ant of our gardens. They are called driver-ants because they drive before them every living creature. There is not an animal that can withstand the driver-ants. In their march they carry destruction before them, and every beast knows instinctively that it must not cross their track. They have been known to destroy even the agile monkey when their swarming host had once made a lodgment on its body, and when they enter a pigstye they soon kill the imprisoned animals, whose tough hides cannot protect them from the teeth of the driver-ants. Fowls they destroy in numbers, killing in a single night all the inhabitants of the hen-roost, and having destroyed them have a curious way of devouring them.'
It appears according to the experiments of the Rev. Dr. Savage, that the ants begin at the base of the beak, and pull out the