The swimming legs are, roughly speaking,
shaped—that is, they consist of a stem, carrying two many-jointed filaments, fringed with fine plumose hairs. A hair is said to be plumose when it bears smaller and finer hairs on each side. ‘By folding the tail beneath the body, and suddenly striking it out again, those animals which exist in the water, as well as those which live on the shore, are enabled to dart or leap to a considerable distance[50].’
Fig. 73.—Nest-building Amphipod. (From life.)
Our hand lens may be well employed in watching some of the nest-building Amphipods at work in the aquarium. There can be no difficulty in keeping these creatures in captivity, and under observation, as they build their tubes and rear their families. They are plentiful in every rock pool round the coast, and it would be a hard matter to dip the net into any such pool without getting a few specimens.
They need absolutely no care. The aquarium of the specimen figured was a four-ounce bottle, tightly corked; and in it was a spray of Cladophora, on which the animal fed, and the growth of which broke up the carbon dioxide and set free good store of oxygen. Here it lived for some months, and built more than one tube for itself against the side of the bottle.
It is easy enough through the pocket lens to watch the Amphipod at work. Like other builders, the first thing it does is to get its materials ready. Lying on its side, with its back against the glass, it will rake together with its antennae and jaw-feet a good store of vegetable débris, or if there be no supply of this, will break off branches from the growing weed.
But gathering vegetable débris, or even filaments of living weed, is very far from being tube-building. Something more is needed to bind the mass into a coherent structure. This the animal itself supplies. The bases of the first two pairs of walking feet are large, and contain glands which secrete a glutinous cement, that can be spread like mortar, or spun out into threads.
An American observer devoted much time to the observation of these animals. He says[51]: ‘When captured and placed in a small zoophyte trough, with small branching algae, the individuals almost always proceeded at once to construct a tube, and could very readily be observed under the microscope.... The branches were not usually at once brought near enough together to serve as the framework of the tube, but were gradually brought together by pulling them in and fastening them a little at a time until they were brought into the proper position, where they were firmly held by means of a thick network of fine threads of cement spun from branch to branch. After the tube had assumed very nearly its completed form, it was still usually nothing but a transparent network of cement-threads woven among the branches of the weed.’