particularly since they do not swim so well " as to bestar with their phosphorescent splendour the vast surface of the ocean, and transform it into a sea of flame," -a spectacle, continues Humboldt, "which stamped upon my memory an ineffaceable impression, and always excited fresh astonishment, although it was renewed every night for months together. It may be seen in every zone; but those who have not witnessed it within the tropics, and above all upon the main ocean, can form but a very imperfect conception of the grandeur of the phenomenon, particularly if the spectator places himself in the shrouds of a ship of the line, during a fresh breeze, when she ploughs through the crests of the waves, and at every roll her side is raised out of the water enveloped in ruddy flames, which stream like lightning from the keel, and flash towards the surface of the sea. At other times, the dolphins, while sporting in the waters, trace out sparkling furrows in the midst of the waves *" Leaving out of our consideration as inadmissible, the opinion of Le Gentilt and Forstert, that the light in question arises from electricity excited by the friction of the water upon the sides of the advancing ship, the ascertained facts appear to be the following. There are several luminous mollusca which have the faculty of emitting at pleasure a feeble phosphorescent light, generally of a bluish colour. Three of these have been particularized, (Nereis noctiluca; Medusa pelagica, ß §; and Monophora noctiluca,) the latter discovered by M. Bory de St. Vincent in Baudin's expedition ||. Besides these, a *Humboldt, Tableau de la Nature, vol. ii. p. 9, and Note. Remarks made in a Voyage round the World, p. 57. number of microscopic animalcules of species still undetermined, which Forster found swimming in innumerable multitudes in the sea near the Cape of Good Hope, have been confidently asserted to be the cause of the phenomenon. But though these may be partly or sometimes the cause, yet, in the greater number of instances, no animalcules whatever can be discovered in the luminous water, even by the aid of the best glasses. Such was the decision come to by Humboldt from numerous observations in the tropical seas, and his authority is one of the highest which can be adduced. We had recently an opportunity of repeating these observations at Hâvre de Grace, and could not discover the slightest trace of animalcules, although the water which we examined was so strongly luminous, that it shone upon the skin of some night-bathers like scattered clouds of lambent flame, appearing more as a property of the water itself than anything extraneous diffused through it; but we particularly remarked that no light appeared in quiescent water, it being only seen when the * Humboldt, Tableau de la Nature, ii. 90. surface was broken by the ripple of the tide, or when a wave dashed upon the pebbles on the beach*. Humboldt, however, is of opinion, that though the phenomenon is only at times caused by animated lamp-bearers, it may probably arise in general from the decomposed fibrillæ of dead mollusca which abound beyond all calculation in the bosom of the waters. He proved this by passing some of the luminous water through cloth, when some of the fibrilla were separated, and appeared in the form of luminous points. We should, on the other hand, have been inclined to infer that these points were caused by the luminous water moistening the fibres of the cloth: and our author himself afterwards seems to abandon the notion of fibrillæ for that of a gelatinous fluid produced by the decomposition of the dead bodies, and imparting to sea-water the nauseous taste, which is as much disliked by us as it is relished by the fishes. Water may thus be rendered luminous by throwing into it a quantity of herring brine, and hence it appears that salt is indispensable; for, as M. Bory de St. Vincent justly remarks, the waters of our lakes and marshes are never luminous, though these abound with polypi, both living and dead. There seem also to be certain states of the air favourable or unfavourable to the development of the light; for one night it will appear with great brilliance, while on the following, though the circumstances seem all equal, it will be gone. It seems to be more frequent, as Humboldt remarked, "when the sky was thick and cloudy, and upon the approach of a storm." We have remarked it as frequently following as preceding a storm; but it seems to be independent of heat or cold; for on the banks of Newfoundland it is observed to shine with great brilliance during the most rigorous frosts. * J. R. Ir may be perceived from some of the preceding details, that insects differ very considerably from the larger animals in their modes of pairing; but there are several species in which the peculiarities are much more remarkable. In the case of moths we have seen the extraordinary phenomenon of life itself being extended several weeks beyond its natural period when a mate could not be met with; and in butterflies it is probably extended to several months; in the case of those females (Vanessa To, V. Urtica, Gonepteryx Rhamni, &c.) which are hatched late in the autumn and live till they meet with a mate in the ensuing spring; while, had they been hatched a month or two earlier, and had left a progeny to supply their place, they would have infallibly died. n PAIRING OF APHIDES. THE earlier naturalists observing that aphides were always found where ants abound, concluded, without further investigation, that the ants shed upon the leaves of plants a sort of plastic humour, from which the aphides were generated*, on the same principles as they erroneously imagined flies to be produced from dead carcasses †. But miraculous as this would have been had it been the case, it is perhaps surpassed by the actual facts which have been ascertained by subsequent observations con*Gödart, ii. Exp. 22. + See Insect Transformations, chap. i. ducted in the most rigid scientific manner-Nature, as is well remarked by Bonnet, having sown them upon all sorts of plants and trees, to provide food for other species of insects, as we sow grain for our own subsistence*. In a word, it appears that the old opinion maintained by Leeuwenhoeck, Cestoni, and Bourguet, which maintains aphides to be generated without pairing, is partially true. Réaumur, in consequence of repeated accidents, was unsuccessful in his observations; but Bonnet, by extraordinary patience and care, succeeded beyond what could have been anticipated. We think his experiments cannot fail to prove interesting. Upon a leafy branch of spindle-tree (Euonymus), plunged in a phial of water, and set in a garden-pot, he placed an aphis which he had seen born the instant before of a mother without wings; and having previously examined the leaves and stem with the most minute care lest there might be any other aphides upon them, he covered the whole with a glass vessel, the edges of which being plunged into the mould, he felt as confident that he had the control of the conduct of his prisoner as Acrisius did as to the actions of Danaë when he shut her up in a brazen tower. This was done on the 20th of May at five in the evening; and he continued to watch with a magnifying glass the imprisoned insect every day from hour to hour, beginning about five in the morning, and leaving off about nine or ten at night, noting its every movement in his journal. It changed its skin four times, in the same manner as caterpillars, and during the last moult it caused our ingenious experimenter not a little uneasiness, from its appearing as if it were preyed upon by internal parasites †, as in that case he would have *Insectologie, Œuvres, i. 10. See Insect Transformations, page 57, &c. |