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Show 18 ADDITIONAL NOTE. V. AMPIIIDIOUS ANIMALS. So stil the Diodons, amphibious tribe, With twofold lungs the sea and air imbibe. CANT. I. J. 331. D. D. GARDEN dissected the amphibious creature called diodon by Lil'meus, and was amazed to find that it possessed both external gills and internal lungs, which he described and prepared and sent to Linneus; who thence put this animal into the order nantes of his class amphibia. He adds also, in his account of polymorpha before the class amphibia, that some of this class breathe by lungs only, and others by both lungs and gills. Some amphibious quadrupeds, as the beaver, water rat, and otter, are said to have the foramen ovale of the heart open, which communicates from one cavity of it to the other; and that, during their continuance under water, the blood can thus for a time circulate without passing through the lungs; but as it cannot by these means acquire oxygen either from the air or water, these creatures find it frequently necessary to rise to the surface to respire. As this foramen ovalc is always open h1 the fret us of quadrupeds, till after its birth that .it begins to respire, it has been proposed by some to keep young puppies three or four times a day for a minute or two under warm water to prevent this communication from oue cavity of the heart to the other from growing up; whence it has been thought such dogs might become amphibious. It is also believed that this circumstance has existed in ·some divers for pearl; whose children arc said to have been thus kept under water in their early infancy to enable them afterwards to succeed in their employment. But the most frequent distinction of the amphibious animals, that live much in the water, is, that their heart consists but of one ceH; and as they are }Jale creatures with but little blood, and that colder Anzpllibious Animals. 19 and darker coloured as froo·s a1Jd I' . -1 1 . ' ' JZaJ c s, t 1ey rcqmrc 1c than the warmer animals with a o· . , ss oxyo·en bl d. d I • oreater quantity and more scarlet oo ' an t lence, though they have on! luno· 1 .. under water witho t 0 • • • Y o·' t ley can stay lo no· Ll oreat mconvemencc. hut arc all of tJ 1'1· froo·s and crocod '] I 1 ' 1em, I \e 1 o ' c . I cs, anc w 1ales, necessitated frcqueJltly to rise aho,·e t 1e SllfHLCC for au·. In this circumstance of th ir possessino· a one-celled colder l 1 1 ll 1 _ "' heart, anJ anc car <.er ) ooc' they approach to tbe state of fis1 . I . ·1 thus ar)pear not t . l, w ll( ] • o acquJrc so muc11 oxyo·cu by their o·ills fro t1 ' water as t t · I · I 0 o m 1c erres na amma s do by thci r llllws fi·onl tllc . t I ] . o .t mosp 1er · w lencc I: ma~ be concluded that the gills of fish do not decompo ~ the watet whrch passes through them, and which contains so mucl1 more oxyge~ than the air, but t1w.t they on Jy procure a small quantit of oxygen from the air wh ich is diffused in the water· vhich 1 ! further fi. d . . ' a so Js . con 1 ~11e by an cxpcnmcnt w1th the air-pump, as fish soon che when put m a glas~ of water into the exhausted receiver which they. would 11ot do if their gills had power to decompose the w~ter and oLtam the oxygen from it. _The lamprey, petromyzon, is put by Linneus amm1gst the nantes whtch are defin_ed to pos cs both gill a11d lungs. It has seven spira~ cula, or breatlung holes, on each side of the neck, and by its more perfect lungs approaches to the serpent kind· Syst N" t 1~1 . . ' · '" . 1c means by wlucl~ 1t adheres to stones, even in rapid streams, is provably owino· to a partial vacuum mad~ by i.ts rc piring organs like sucking, and ~1~y be compare~! to the 1ngemons method by which boys are seen to lrft large stone 111 the st reet, by applying to them a piece of stron o· ~1oist 1:ather with a string throuo·h the centre of it; whicl1, when i~ IS forcibly dr't\\'n upwards, produces a partial vacuum under it, and thus the stone is supported by tl1e pressure of the atmosphere. . The leech, hirudo, and the remora, echencis, adhere stro11gly to OOJCCts probably by a sim ilar methocl. ·I once saw ten or twelve leeches adhere to each foot of an old horse a little abo,,e his hoofs who was grazing in a morass, and which did not lose their hold when' he moved about. The bare-legged travc11crs in Ceylon are said to be much infested by leeches; and the sea-leech, hirudo muricata, is said |