Page:Encyclopædia Britannica, Ninth Edition, v. 2.djvu/296

Rh 276 AKACHNIDA [ACARIDS. Fam. 2. Tanurides (ra.va.6s, long, cvpa, a tail). The type of this family is Dcmodex folliculorum, Simon (fig. 3), a very curious parasite found in the follicles of the iiurnan nose hence its specific name. a -^5f^ cr It is long and slender ; the abdo- jnen drawn out into a wormlike tail ; the fore part or cephalo-thorax Jus in the adult state four pairs of rudimentary legs, in the immature state three pairs. This is one of the lowest forms of acaridians, and pre sents in its adult state the immature vermiform appearance of the higher genus Typhlodromus (Packard, Lc.) Fam. 3. Tardijradidcs. Body cylindrical, vermiform, but with no FJG. 3. Demodex folliculorum, distinct abdomen ; it is furnished Simon; under side. a. ..a, rndi- throughout its whole length with mentary legs; &amp;gt;, abdomen. four pairs of rudimentary limbs, of which the fourth pair is quite at the posterior extremity; eyes, two ; falces, style-like. These animals are microscopic in size and aquatic in habits; they are hermaphrodite, and are now generally held to be acarids of a very low grade (Packard, I.e., p. 668). Several genera have been char acterised. Fig. 4 represents Milncsium tardigradum, Schrank. Fam. 4. Acnrides. We now come to the more typical forms of Acaridea. The family Acarides have a soft, thin-skinned body, with the thoracic junction often visible ; falces either s-jissor-like or styliform ; maxillas obsolete ; legs of the two first pairs often widely distant from those of the lander ones ; in some lowly organised forms, &quot;face-mites,&quot; four legs only are found ; perhaps these are the immature form of some other species &amp;lt;?); eyes, none. In this family are included the chcsse, itch, and sugar mites, with numerous others parasitic on various animals. Some fonns, as Hderopus ventricosus (Newport), Dermalcichus, and Typhlodromus, particularly in the immature state, ixhibit an evident link between the last two families and the higher acarids ; on the agamic reproduction ser., i. p. 236. Fam. 5. Oribatid?s. Body hard and horny ; the thoracic junctions generally with two wing-like pro jections and two or three cup-shaped pedicellated stigmata on the edge, leading to the respiratory tubes. The Oribatides in general live on vegetable matter, and several genera have been characterised. The immature forms of many species vary greatly from the adults, so that numbers have been described as distinct species. See on this family an elaborate paper by M. H. Kicolet, in the Arch, du Mus., t. vii. pp. 383-482, pis. 24-33. Fam. 6. Gamasides. Body, oval, flattened ; epidermis, dense ; fdces, scissor-like ; maxilke, free ; legs, equal in size and of similar form ; eyes,_ obsolete. There are several genera of this family para sitic on various animals. Fam. 7. Ixodidts. Body, round, oval, or somewhat oblong, of a leathery consistency ; palpi, short, three or four jointed ; falces, saw-like, and, with the other parts of the mouth, joining in the for mation of a beak for thrusting into and holding on to their prey. Eyes, often obsolete; legs weak. On the generation of Ixodes, see a paper by Prof. Gene, communicated by A. Tulk to Ann. and May. X. H., No. 188, Sept. 1846, p. 160. When gorged with the juices of their victim the abdomen attains an enormous size, and appears almost to obliterate all the rest of the body. In this family are comprised the &quot;ticks&quot; (Ixodes), which are often so tormenting to mankind, and domestic and other animals (figs. 5, 6). Among these ticks is included also the noted genus Argas, of which a species, A. reflexus (Latr.), has lately been found at Canterbury, England. Some of the largest known acarids are contained in this family. Fam. 8. Hydrachnidcs, or water-mites. Body, oval, or almost globular; palpi, short; legs, ciliated for the purpose of swimming ; eyes, two. These acarids are found in salt as well as in fresh water. Some are parasitic, when immature, on water-bugs and water-beetles ; others, through life, on the gills of the fresh-water mussel. Fam. 9. Tro/nbidides. Body, stout, round, or oval, and often somewhat oblong; frequently broader before than behind; some times clothed densely with a kind of pubescence. The two hinder pairs of legs far removed from the two fore pairs. Eyes, two. The colour of the species of this family is generally of a bright red. FIG. 5. Ixodes xgyptius, Savicny. a, falces; b, b, palpi ;c, caput; d, cephalo- thorax. c, abdomen. scarlet, or yellowish. Among them is the red mite, Tctranychiis telarius (Linn.), popularly called the &quot; red-spider,&quot; which infesta hothouses. Fie. C. The same ; under side, a, falces ; 6, 6, palpi ; f, genital aperture ; d, anal orifice;, e,/, maxillae and labium soldered together; g, sternum. Fam. 10. Bdcllidcs. Body, oblong-oval, showing the junctions of caput, thorax, and abdomen ; palpi, long ; eyes, two to six, sometimes obsolete ; legs, long and strong ; parts of the mouth forming a tapering pointed beak of greater or less length, and looking like a prolongation of the caput. The Bdellides live in damp places, under moss, &c., and on the floors of caverns. The above characters of the Acaridian Families are abridged chiefly from A. S. Packard s Guide to the Study of Insects. Besides Claparede s Studien an Acariden, and Nicolet s Memoir -e on Oriba tides, and other works above noted, may be mentioned Dr C. Heller on the anatomy of Argas persicus, Sitzungsb. d. K. AJcad. d. W. Math. Naturw. Cl. Bd. xxx. No. 15, 1858, pp. 297-326, Taf. i.-iv. , Charles Robin s Memoire zoologique et anatomique sur diverscs especes- d Acaricns de la Famillc des Sarcoptes, 1860, with 8 plates ; also by- same author, &quot; Memoire sur les Sarcoptes avicoles, et sur les metamorphoses des Acariens,&quot; Comptcs Rendus, torn. Ixvi. pp. 776 786 ; H. A. Pagenstecker, Bcitragczur Anatomic dcr Milben, Heft 1, &quot; Trombidium,&quot; 2 Taf. 32 pp., Leipsic, W. Engelman, 1860 ; P. J. van Beneden, &quot; llecherches sur 1 histoire naturelle et la developpe- mentde 1 Atax Ypsilophoms (Hydrachna concharum),&quot; Nouv. Mem. dcl Acad. de Beige., torn. xxiv. 1850 (24 pp. ed. 1. pi.) Of the older works on Acaridea maybe mentioned that of Hermann, Mlmoirt Apicrologiquc, in fol., Strasbourg, 1804 ; and P. Gervais, in Walcke- naer s 7ns. Apt., torn. iii. pp. 132-288, pis. 31-36 and 38, 1844 ; Doyere, &quot;Memoire sur les Tardigrades, &quot; Ann. Sc. Nat., 2 scr. &quot; Zool.,&quot; torn. xiv. 1840, pp. 269-361 ; Suite, Ibid., torn. xvii. 1842, pp. 193-205, and torn, xviii. 1842, pp. 5-35, with 8 plates; P. J. van Beneden, llecherches sur 1 organization et la de veloppement des Linguatulcs (Pcntastoma, Eud.) suivies,&quot; &c., 39 pp. with 1 pi., iffl Nouv. M6m. de I Acad. dc Beige } torn, xxiii. 1849. Order II. PYCNOGONIDEA. The creatures of this order form a small group which it appears now necessary to receive among the Arachnida,