CLASS A EACH N I DA. 



ORDER AC AR I DA. MITES. 



147 



CLASS VIII. ARACHNIDA. 



THE trunk or body of this Class, differing as to the solidity of its external covering in its several Orders, consists either of two distinct 

 though connected regions, or is but one undivided whole. In the former case, the anterior region includes the head and thorax 

 undistinguished from each other by definite boundary, and therefore called the cephalo-thorax, whilst the posterior region is the 

 abdomen. 



ILLUSTRATIVE EXAMPLES. 



PLATE ABACHNIDA. 

 ORDER I. THYSANOURA. FRINGED-TAILS. 



FORBICINIA. (of Geoffrey), or LEPISMA (of Linnaeus). Eyes small, far 

 apart, composed of granulations ; body flattened, and ending in threads of 

 the same length, inserted on the same line, and not raised in leaping. Body 

 long, and covered with bright, silvery scales, which are longitudinally 

 striated ; they have lately been used as a test for the goodness of micro- 

 scopes. 



Type of the genus, L. Saccharina, found in damp places. 



Illustration : Forbicina vittata. 



PODURA. Antennae short, straight, four-jointed ; palpi inconspicuous ; 

 body apterous, cylindric ; abdomen elongate, linear ; tail furcate, inflexed 

 beneath the abdomen. 



Type of the genus, P. plumbea, found with the other species, which are 

 extensive in damp places, beneath stones. 



Illustration : Podura villosa. 



Our Plate contains figures of two species of the most common genera of 

 Parasites human and ornithological : 



RIOINUS (Nirraidia of Leech). Antennas five-jointed, filiform; body 

 narrow ; head of moderate size, with the sides rounded, or unangular 

 anteriorly ; abdomen with the last segment entire and rounded in the males ; 

 tarsi curved, triarticulate, with two contiguous, parallel, bent claws. 



Type of the genus, N. discocephalus, Nitzch. A numerous genus living 

 upon birds of all orders ; about fourteen species have been detected in 

 Britain. 



Illustration : Ricinus pavonis. 



PEDICULUS. Apterous; antennae short; mouth produced into a very 

 short, tubular haustellum ; thorax distinct, not narrower than the abdomen, 

 which is linear ; tarsi didactylous. Of this unsightly genus two species are 

 found in Britain. 



Type of the genus, and 



Illustration : Pediculus humanus. 



ORDER II. ARANEIDA. SPIDERS. 



ILLUSTRATIVE EXAMPLES. 



MYQALE. Palpi projecting, pediform, inserted at the extremity of the 

 jaws ; mandibles robust, with their points bent downwards ; jaws two, 

 elongated ; labium small, quadrate ; eyes eight ; body large ; legs lone, 

 stout. 



The species are of large size, but not very numerous ; they build their 

 nests of silky tubes or bags in holes in the ground, or in trees. The type 

 devours ants, and sometimes, it is affirmed, small birds ; the latter inhabits 

 South America. 



Type of the genus, and 



Illustration : Mygak avicularia. 



AKANEA. Eyes eight, disposed in two transverse lines near each other, 

 and bent somewhat backwards. Maxillas straight, longitudinal, of equal 

 breadth, apex rounded, inner angle truncated. Lip nearly quadrate, of 

 about equal length and breadth, becoming gradually a little narrower 

 towards the superior angles. The fourth and first pairs of feet of nearly 

 equal length, and longer than the second. 



The habits of the different species of Spiders are, perhaps, as interesting 

 as those of almost any other tribe of animals ; and the ingenuity with which 

 some of them form then- beautiful geometrical web, has in all ages excited 

 the admiration of the most casual observers of nature, and supplied allusions 

 and illustrations to the moralist and the poet. 



Illustrations : Aranea extensa, A. lobata. 



ORDER III. CHELIFERA. SCORPIONS. 



ILLUSTRATIVE EXAMPLES. 



SCORPIO. Head, thorax, and abdomen united, forming an elongate-ovate 

 mass; mandibles short, rounded, narrow, hirsute; legs twelve, anterior 

 pair extremely short, second pair much elongated, the last joint, thickened 

 at its apex, armed with forceps, the remaining four pair formed for walking, 

 and resembling each other ; eyes six or eight, two large approximating ones 

 on the disc of the thorax behind, and two or three small contiguous ones 

 on each side of the anterior lateral margin; breast with two pectinated 

 plates ; tail six-jointed, the terminal joint armed with an elongate, curved 

 spine, perforated near the apex for the passage of poison. 



Type of the genus, S. Eurap&us, Scopoli. A numerous and disgusting 

 tribe of animals, very abundant in the hotter regions of the globe, though 

 in very warm summers individuals have been found in the ports of England. 



Illustration : Scorpio rufescens. 



CHELIFEK. Mandibulae short, apex didactylate ; palpi two, very long, 

 of five articulations, broken, having pincers at the apex ; maxillae two, con- 

 nivent ; eyes two or four, inserted at the sides of the thorax ; body ovate, 

 rather acute before, depressed; the abdomen ringed ; feet eight, the tarsi 

 with two claws. 



These little animals, which in form somewhat resemble a minute scorpion 

 without a tail, are found under stones, the bark of trees, &c., or in houses 

 amongst old papers or in holes in walls. They feed on the carcases of 

 insects, or on any dried animal substances, and occasionally on Woodlice or 

 Flies, on which they are parasitic. 



Type of the genus, and 



Illustration: Chelifer cancroides. 



ORDER IV. ACARIDA. MITES. 



ILLUSTRATIVE EXAMPLES. 



SMARIS. Palpi small, filiform, straight, simple ; mouth porrect, elon- 

 gated into a beak; eyes two; body oval, scaly; legs not formed for 

 swimming, eight in number, the anterior pair longest, four posterior some- 

 what remote. 



The type of the genus, S. Sambuci, inhabits various parts of Europe, and 

 is taken occasionally in England. 



Illustration : Smaridia fringfllaris. 



SIRO. Body oval ; palpi two, five-jointed, the joints elongate ; mandibles 

 two-jointed, cylindrical, compressed, and forcipated ; eyes two, placed on a 

 peduncle on each side of the thorax ; legs eight, elongate, filiform ; tibiae 

 and tarsi two-jointed, terminated with a bent claw. 



Found in France and England, at the roots of trees, beneath mosses. 



Type of the genus, and 



Illustration : Siro rubens. 



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