DIPSACEjE DIPTERA. 



287 



and the raising of the wings, converts these into levers 

 for the depression of the body ; and by this means it 

 gets very speedily under water, so speedily, indeed, 

 that it appears to run down the bank to the bottom 

 with no more apparent effort than what is necessary 

 for simple progressive motion. When it is overhead 

 in the water, the wings, and partially also the head are 

 used with great neatness and effect ; and the upward 

 stroke of the wings, even in that case, serves to keep 

 the body to the bottom against any difference of gra- 

 vitation there may be between the bird and the same 

 bulk of water. In this way it can pick up and even 

 pursue its food below water as easily as a common 

 ground bird can do on the surface of the earth ; and 

 as, when below the surface, it always holds the wings 

 recovered, that is, at such a distance from the body 

 as that they can strike first either upwards or down- 

 wards, it can move with equal celerity in any direction. 

 This need excite no surprise ; for though wings are 

 not the usual instruments of motion below water, yet 

 the difference between the wings in the air and in the 

 water is more a question of their being proof against 

 the action of water than of any thing else, because in 

 the matter of specific gravity, it requires no very great 

 degree of mechanical acumen to perceive, that it is 

 not more difficult for a bird, by muscular exertion, to 

 keep itself down in a fluid specifically heavier than 

 itself, than it is to keep itself up in a fluid specifi- 

 cally lighter ; and, as the difference between the spe- 

 cific gravity of the dipper, and that of water, is really 

 less than the difference between the specific gravity 

 of any bird and air, the dipper has an easy task. 

 We forgot to mention that the dipper is a sort of song- 

 ster in the early part of the year, though not a very 

 melodious one ; yet it is cheerful to hear a bird sitting 

 on a stone in the brook and singing, when the banks 

 of that brook are covered with snow. The summer 

 note is a mere chirp. 



DIPSACE^;. The teasel or scabious family, a 

 natural order of dicotyledonous plants, containing 

 eight genera, and nearly one hundred and twenty 

 known species. It is closely allied to Composites, but 

 differs in its distinct stamens and pendulous albu- 

 minous seeds. It also bears an affinity to Calycereee, 

 from which it is distinguished by its free anthers and 

 inverted embryo. It bears likewise a relation to 

 Valerianeee, but differs in its habit, its capitate flowers, 

 and in having an involucellum. By these characters 

 it is also separated from Caprifoliacece. 



Its essential characters are : calyx superior, mem- 

 braneous, resembling pappus, surrounded by a scarious 

 involucellum. (This involucellum is a peculiar organ, 

 resembling an external calyx, and may be said to cor- 

 respond in some degree with the partial involucre ol 

 the umbellifertf.) Corolla monopetalous, tubular, in- 

 serted in the calyx ; limb oblique, four or five lobed, 

 with an imbricated aestivation ; stamens usually four, 

 inserted into the tube of the corolla, alternate with it 

 lobes ; anthers distinct, two-celled ; ovary inferior, one- 

 celled, with a single pendulous ovule ; style filiform ; 

 stigma simple, longitudinal or capitate ; fruit dry, in- 

 dehiscent, one-celled and one-seeded, crowned by a 

 pappus-like calyx ; albumen fleshy ; embryo straight 

 radicle superior. 



The plants belonging to this order are herbs or 

 undershrubs, with opposite or verticillate leaves, and 

 densely capitate flowers, which are surrounded by a 

 many-leaved involucre. 



They abound in the soutn of Europe and north o 

 Africa. Some are also found at the Cape of Good 



Hope and the Levant. In general they shun cold, 

 and do not reach a great elevation above the sea. 



Their properties are not deserving of much atten- 

 tion. Many of them are bitter and tonic, some are 

 used on account of their astringency in dyeing, and a 

 Few possess febrifuge virtues. 



The chief genera of the order are Dipsacus, Scabiosa, 

 Knautia, Marina, and Pteroccphahis. 



The genus Dipsacus, or teasel, includes thirteen 

 species, of which three are natives of Britain. Dip- 

 sacus fullonum, fullers' teasel, is so called on account 

 of being used in dressing cloth, for which purpose the 

 hooked scales of its receptacle are admirably adapted. 

 These are fixed round the circumference of a large 

 broad wheel, which is made to revolve, while the cloth 

 is held against them. By long cultivation in a poor 

 soil, the hooks of the receptacle are said to disappear. 

 By some botanists this species is looked upon merely 

 as a variety of Dipsacus sylvcstris, or the common wild 

 teasel. Dipsacus pilosus, small teasel, is the hanu 

 sorriest species. Its seeds are eaten by small birds. 

 The axils of the leaves of the common teasel usually 

 contain a quantity of limpid water, which is sometimes 

 very acceptable to travellers. 



The genus Scabiosa, or scabious, includes sixty-one 

 known species,only two of which are natives of Britain. 



Scabiosa succisa, Devil's-bit scabious, is common in 

 meadows and pasture land. It derives its name from the 

 circumstance of its root being as it were cut or bitten 

 off abruptly. It is said to yield a green dye, and also 

 to be sufficiently astringent for tanning. 



Scabiosa alropurpnrca is rather a handsome species, 

 bearing dark purple flowers, and is cultivated as a 

 border annual or biennial. The leaves of Knautia 

 arvensis, common field scabious, have a sharp and 

 rather bitter taste, and were formerly recommended 

 in cutaneous diseases. 



DIPSACUS (Linna3us). A genus of European 

 herbs, one of which is the well-known clothiers'-brush, 

 or teasel, found wild as well as cultivated in England. 

 It belongs to the fourth class and first order of Lin- 

 naeus, and gives a title to an order in the natural sys- 

 tem, namely, Dipsacecc. Some of the species are 

 admitted into the flower-garden, and are raised from 

 seeds. The cultivated teasel is, like the rest, a bien- 

 nial, and is sowed in drills, and kept clean and 

 thinned by the hoe in the first year ; in the second, 

 the plants are also kept clean, and when the heads 

 are ripe, they are cut for sale. 



DIPS AS (Leach). A genus of molluscs now 

 forming a subdivision of the genus ANODON, under 

 which it is described. 



DIPTERA. An order of insects belonging to 

 the great division Haustellata, or those furnished with 

 a tubular proboscis, and distinguished by the presence 

 of only a pair of membranous extended wings affixed 

 to the centre of the sides of the thorax, and generally 

 furnished near their insertion with a pair of short 

 clubbed organs, termed halteres or balancers, respect- 

 ing which, as. analogically representing the posterior 

 wings of the four-winged insects, entomologists are at 

 variance ; the mouth is provided with a sucker com- 

 posed of from two to six scaly lancet-like pieces, and 

 enclosed in a canal upon the upper surface of a fleshy 

 proboscis, or covered by one or two inarticulated 

 plates which serve as a sheath (Hippobosca). The 

 body is composed, as in the other six-legged insects, 

 of three principal divisions representing the head, 

 thorax, and abdomen. The ocelli, when present, are 

 generally three in number ; the antenna 1 exhibit various* 



