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of water. Comparatively shallow cases are preferable, composed partly of slate, for the sake of coolness and moderate light. Though square in form exteriorly, the case may have a sloping interior from front to back, on which the animals are placed. The keeping of the water free from impurities is of the utmost importance, and for this purpose all dead animals and floating waste matter should be removed with a feather, sponge-stick, or hand-net. Nor is it less necessary to maintain the due specific gravity of the water, in the salt-water aquarium, for as it becomes more dense or strong by evaporation, fresh additions require to be made. The proper density of sea-water is, of course, that of water taken from the ocean; and at this point it can be maintained by noticing a glass specific-gravity ball, which may be kept afloat on the surface—the ball rising as the density increases. Where natural sea-water cannot be obtained, an artificial kind may be made by a compound of common table-salt, 3} ounces; Epsom salts, quarter of an ounce; chloride of magnesium, 200 grains troy ; and chloride of potassium, 40 grains troy;
the whole dissolved, and liquor poured off clear from grounds, and then poured into fresh water until it register 1'027 by the hydrometer.
The Water-Spider (Argynoreta aquatica) is an interesting inmate of the fresh-water aquarium. It is a true spider, but remarkable for living mostly under water. The abdomen is covered with a kind of fur, which repels the water, and retains a bubble of air, so that
the skin does not get wet, and the air-tubes, by which the spider breathes, are sufficiently supplied. Under water, the creature seems to be surrounded by a silvery pellicle. It sometimes comes out of the water, to chase insects, which are dragged into the water as soon as they are caught. The owner of the aquarium may have the
pleasure of seeing the spider make nests for its residence, carrying down little bubbles of air from the surface at the extremity of its abdomen, by means of filaments which are situated there, and depositing them in a curious manner, by touching the edge of the plant to which the nest is to be attached. And so it proceeds, bringing down bubble after bubble, and weaving a web around them, within which it afterwards lives. Near the mouth of this nest, webs are made to float in the water, for the capture of water-insects, just as other spiders make their webs in the air. Sometimes the insects captured are brought to the surface to be devoured, sometimes they are carried into the nest. When the water-spider is placed in a jar, in which there are no water-plants, the nest is either affixed to the edge of the jar, or suspended by means of threads carried from one side of it to the other. Many interesting things may be observed in the natural history of the water-spider, and not the least interesting is the nest which' it makes for its young. The eggs are deposited under water, enclosed in a web thicker than that of the spider's own ordinary residence, and much tougher and stouter, the roof also being much thickened.
As an aquarium requires almost constant attention, it is proper to say that no one should attempt to keep one who is not prepared to give it the due degree of consideration and management. Where, as in the case of the Zoological Society of London, a public institution is inclined to undertake the cost and trouble of maintaining aquaria for exhibition, no objection can be made, and so far they may be successfully kept. Mr Lloyd, however, discommends their being introduced as part of the attractions of ordinary conservatories; the brilliant light and other conditions required for ordinary greenhouse plants being destructive to the plant-animals in an aquarium. On the whole, the simple parlour or drawing-room aquaria are the kinds which are most successful. Nor need any one refrain from indulging in this amusement on account of the dinginess of his dwelling. 'A room,' says Mr Lloyd, 'on the first floor of a house in a densely-populated part of London, closely surrounded by high buildings, with one window facing due east, glazed with ground glass, and having its aperture of an area equalling only one-twelfth of the area of the four walls of the apartment, is found to yield ample light enough for several flourishing aquaria. The same result is attained in another room, with a due west window, glazed with fluted glass, of an area of only one-twentieth of that of the walls. These are actual instances, cited in opposition to the conservatory notion.'
It should be added, that the collecting of marine plants and zoophytes on rocky shores at times of low water may form an amusing occupation, and serve to relieve the tedium which is not unusually experienced at sea-bathing quarters. Instructions how to select, preserve, and carry away these gatherings, will be obtained from the manuals to which we have referred. In various places,
retired officers of the preventive service make a kind of business of gathering zoophytes, and offering them for sale at most inconsiderable prices. While (1861) at Ventnor, in the Isle of Wight, we found one of these obliging persons (Mr Matthew Hale) engaged in this occupation; and from his varied and interesting stock, he offered to send anemones and other specimens to any part of England, packed in wet sea-weed, which he declared kept them more lively and free from damage than if sent in jars of sea-water. As amateur-keepers of aquaria will not disdain to pick up. practical information wherever it is to be found, they need hardly be recommended, when at the sea-side, to make the acquaintance of all such professional collectors.
Since writing the above, we have seen a very interesting work, amply illustrated, on the same subject-namely, the Aquarium of Marine and Fresh-water Animals and Plants, by G. B. Sowerby, F.L.S. London : Lovell Reeve, Henrietta Street, Covent Garden.
THE INSECT VIVARIUM.
After the invention of the Wardian case, and of the Aquarium, the idea of the Insect Vivarium could not fail soon to suggest itself. Entomologists have long been in the practice of rearing caterpillars and other larvæ, keeping them in boxes and supplying them with their appropriate food, so as to enjoy opportunities of observing their transformations, and to obtain the perfect insect as a specimen for the museum. And thus have entomological collections been furnished with butterflies in all their splendour; ruthlessly killed, however, shortly after their emerging from the chrysalis, ere yet the lustre of their wings has been dimmed, or any of the fine scales rubbed off, as is apt to be the case with butterflies captured in their flight in groves, meadows, or moors. From this the transition was easy to an insect vivarium, partly formed of glass, and affording opportunity of observing insects in the different stages of life, whilst at the same time it added another pleasing ornament to the drawing-room or to the apartment of less pretentious name, in which the Spitalfields weaver, for instance, prosecutes the study of entomology; for it is an interesting fact that entomology has long been a favourite pursuit among the Spitalfields weavers, and one in which many of them have been most enthusiastic and successful.
The insect vivarium is made partly of slate or zinc, and partly of glass; the bottom, back, and sides being made of the former material, the front and top of the latter. A minute description is unnecessary; the form may be varied according to taste or convenience. The upper part ought not to be made entirely of glass, as much light is injurious to many larvæ, even of insects which in their perfect state rejoice in the brightest sunshine. But the life of a butterfly or other insect in its perfect state is generally very brief, and the vivarium must rather be adapted to its larval state and the observance of its transformations. There must be a sliding door or other contrivance for ready access to the interior; and a plate of perforated zinc, or something similar, is necessary for ventilation; and to prevent the atmosphere within the case from becoming too moist, to the injury of insect life. The bottom of the vivarium is filled with earth, as in a Wardian case, broken pottery or the like being placed below it to secure rfect drainage, and in the earth are planted tufts of grass, ferns, and other plants suitable to the size of the case, and plants in pots are also introduced as may be found desirable. Tubes of zinc or tin are placed in the earth, to contain
water, and thus to admit of the introduction of twigs of trees or any foliage requisite as the peculiar food of any kind of larva. It is also very desirable to have a portion of the space devoted to water insects, and for this purpose a miniature pond is formed by a watertight partition, and water-plants and pond-snails are placed in it, as in the aquarium, to prepare it for its proper occupants. A few sticklebacks, minnows, or other small fishes, may also be placed in
it, to make it more lively and pleasing. And now the vivarium is ready, and may be stocked with insects as opportunity is found ; water-beetles, and the larvæ of gnats and dragon-flies, may be placed in the pond, and caterpillars may be collected from the garden, the field, or the wood, care being taken to note their appropriate food and to provide them with sufficient fresh supplies. Caterpillars are extremely voracious, and grow with great rapidity. The larva of the dragon-fly is very interesting from its ferocious aspect and habits ; that of the gnat is still more so from its playful gamboling in the water, and its occasional suspending of itself at the surface of the water by the star-like breathing apparatus in which its abdomen terminates. But the variety of interesting objects of study is endless; and a vivarium affords excellent opportunity for observing many of the most wonderful things in nature, and for adding new discoveries to science, whilst the mind of the observer is always agreeably occupied and often filled with new delight as he watches habits and transformations, which, whether known or unknown before, come under his notice at least for the first time. There is no little pleasure to be found in watching the caterpillar as it spins