297 



AREOLAR TISSUE. 



ARGULUS. 



293 



habits afford a close resemblance to those of the earth-worm away from 

 the shore. It is bigger than the earth-worm, sometimes being found 

 nearly a foot iu length. It is of a reddish colour, and when touched 

 throws out a quantity of a yellow fluid which stains the hand. It is 

 employed by fishermen as bait for various kinds of sea-fish. 



AREOLAR TISSUE. The nature of this tissue will be best under- 

 stood if we first describe Fibrous Tissue, of which it may be regarded as 

 a modification. Fibrous Tissue is now usually considered under two 

 heads, namely, as the white and the yellow tissue. White Fibrous Tissue 

 occurs in ligaments, tendons, and membranes requiring great strength. 

 On carefully dissecting away the areolar tissue with which it is asso- 

 ciated, it seems, when examined under the microscope, to consist of 

 extremely delicate fibrillic running parallel to one another, and taking 

 an undulating course. There is however reason to believe it does 

 not in reality consist of a bundle of fibrilte, but that it is simply a 

 mass with longitudinal parallel streaks, and which has a tendency to 

 split up in a longitudinal direction. (Fig. 2, a.) 



Yellow Fibrous Tissue differs in many essential points from the pre- 

 ceding form. It is remarkably elastic, is of a yellow colour, and is 

 arranged in bundles or fibres, invested by a thin sheath of areolar 

 tissue. In man we find it extended between the laminae of the ver- 

 tebrae, in several other ligaments, and in the transversalis fascia of the 

 abdomen. It forms the ligamentum nuchae of animals. Examined 

 under the microscope it is seen to consist of fibres varying in diameter 

 from the 5000th to the 10,000th of an inch. They bifurcate, or even 

 divide into three, and freely anastomose with each other. 



Fig. 1. 



Yellow Fibrous Tissue showing the curly and branched disposition of its fibrilte. 



Areolar Tittue is dispersed over almost every portion of the body, 

 being the substance most commonly (but incorrectly) termed Cellular 

 Tiuue. The following are the microscopic characters of this tissue, 

 as described by Bowman and Todd : " When a fragment is examined 

 it presents an inextricable interlacement of tortuous and wavy threads, 

 intersecting one another in every possible direction. They are of two 

 kinds. The first are chiefly in the form of bands of very unequal 

 thickness, and inelastic. Numerous streaks are visible in them, not 

 usually parallel 'with the border, though taking a general longitudinal 

 direction. These streaks, like the bands themselves, have a wavy 

 appearance, but can be rendered straight by being stretched. The 

 streaks seen have more the marks of longitudinal creasing than a 

 true separation into threads ; for it is impossible to tear up the baud 

 into filaments of determinate size, although it manifests a decided 

 tendency to tear lengthways. The larger of these bands are often as 

 wide as the 500th of an inch ; the smaller can only be detected with 

 high powers. These are the white fibrous element. The others are 



Fig. 2. 



The two elements of Areolar Tissue in their natural relations to one another. 

 a, the white fibrous element, with cell-nnclei, j, sparingly visible in it ; b, the 

 yellow fibrous clement, showing the branching or anastomosing character of its 

 tlbrillx; c, flbrilte of the yellow element, far finer than the rest, but having a 

 similar curly character ; d, nucleated cell-nuclei, often seen apparently loose. 



lung, single, elastic, branched filaments, with a dark decided border, 

 :>Tnl disposed to curl when not put on the stretch. They interlace 

 with the others, but appear to have no continuity of substance with 



them. They are most commonly about the 8000th of an inch in 

 diameter. These form the yellow fibrous element. 



These two tissues may be most easily discriminated by the addition 

 of a drop of dilute acetic acid, which at once swells up the former 

 and renders it transparent, whilst it produces no change in the latter. 

 It thus brings into view 

 corpuscles of an oval shape, 

 which are probably the 

 nuclei of the cells from 

 which the bauds have been 

 originally produced. Oval 

 corpuscles (fig. 2, d), either 

 altogether isolated or hav- 

 ing very delicate prolonga- 

 tions with the adjacent 

 threads, are sometimes 

 noticed. They seem to 

 be either advancing or 

 receding stages of the 

 tissue. 



In Jiff. 3, which repre- 

 sents the Areolar Tissue 

 from beneath the skin of a 

 five-months foetus, we can perceive the cells elongating into fibres. 

 In a chemical point of view the leading difference between the 

 white and yellow tissues is, that the former is acted on by acetic acid 

 in the manner described, and yields a considerable amount of gelatine 

 in boiling ; while the latter resists the action of acetic acid, and yields 

 little or no gelatine. 



ARFVEDSONITE, a mineral belonging to the Hornblende Series. 

 The cleavage is parallel to the lateral planes and both the diagonals 

 of a rhombic prism. The colour black ; fracture uneven ; hardness 

 6'0 ; lustre vitreous and opaque ; and has a specific gravity of 3'4 to 

 3'5. It is found in Norway and Greenland. According to analysis 

 by Dr. Thomson it contains 



Silica 50-508 



Peroxide of Iron 35'144 



Sesqui-oxide of Manganese . . . 8'920 



Alumina 2'488 



Lime 1-560 



Water 0-960 



ARGALI, in Zoology, the name of a species of Wild Sheep (Oris 

 Amman) found on the mountains of Siberia and Kamtchatka. 

 [SHEEP.] 



ARGEMO'NE, a small genus of plants belonging to the natural order 

 Papaveracece, of which three species are cultivated in this country as 

 ornamental plants. They are all natives of Mexico, and are charac- 

 terised by having six petals and three sepals, a very unusual number 

 of parts in the natural order to which this genus belongs. Their 

 leaves are prickly, and generally marked with whitish or pale bluish- 

 green veins ; the flowers are white or yellow. The commonest species is 

 A. Mexicana, from the seeds of which the Mexicans obtain an oil very 

 useful to painters; the handsomest is A. yrandiflora, the flowers of 

 which are pure white, and as much as three inches in diameter. 

 They are all hardy, and will thrive in almost any soil or situation. 

 Their seeds should be sown in a hot-bed, and the young plants treated 

 as half-tender annuals. 



ARGENTINE, in Mineralogy, a white laminated variety of crys- 

 tallised calcareous spar containing a little silica. [CALCAREOUS SPAR.] 

 ARGES (Goldfuss) is the Paradoxidee bimwcronatm of Murchison. 

 ARGULUS, a genus of Entomostracous Crustacea, belonging to the 

 section Pacilo/ioda. There is but one species of this genus, the 

 A. foliaceuK. This little creature is not unknown to fishermen, as it 

 is frequently found parasitic upon various kinds of fish. It was first 

 described by Bilker in his ' Employment for the Microscope," in 1753, 

 under the name of ' The Louse of the Carp and Banstickle or 

 Prickleback.' It 'is about the tenth of an inch in length, and is 

 almost as broad as it is long. The head is in the form of a circular- 

 shapcd shield. The antennae are short, thick, and two-jointed. Instead 

 of a second pair of foot-jaws it has a pair of circular or disk-shaped 

 suckers, by means of which it attaches itself to the animals on which 

 it is parasitic. These suckers are admirably constructed for their 

 use. Four muscles are attached to the base of each of these organs, 

 and extend up by the sides. By this arrangement the creature can 

 make use of these organs, by exhausting the air in the same way as in 

 cupping-glasses, to fasten itself, and also by relaxing the muscles, to 

 walk, when it wishes to change its position. These little creatures 

 are nearly transparent, or of a slightly greenish hue, so that its 

 internal organisation can be readily seen by means of the microscope 

 by transmitted light. The body is marked on both sides by a series 

 of ramifications of a dark colour. The female is larger than the male, 

 and is distinguished, in addition to the ovary, by a black mark on each 

 lobe of the abdomen. 



' The Argulus is found upon various fresh-water fishes. It is most 

 frequently met with near London on the Stickleback, but it has been 

 noticed as occurring on the Carp, the Roach, the Trout, the Pike, the 

 Rudd, and even upon the tadpole of the common Frog. It seems to 

 abound especially when fish are in ill health. 



