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Show 54 ON . CLASSIFICATION. pulmonary sacs, fitted for the breathing of an· directly. B11t then 1nany of the lower Arachnida, like the lower Crustacea, aro devoid of special respiratory organs, and so the diagnosti(· character fails to be of service. Fig. 26. .Fig. ~f:i.-Diagram.mat~c section of a Scorpion, the locomotive members being cut awav. ct, Mouth leadmg mto the pharyngeal pump. The large labrum lies above the mouth and at the si~e of it are the bases of the large chelre, or mandibles, rv., and 11bov~ t?em the chelicera:, 01: antennre. VI. to xx. Somites of the body. T, Telson; b, intest~ ne i. c,. an~s; d, md1?~tes the positi o~1 o.f the. heart; e, the pulmonary sacs; f, a lme mdLCatmg the pos1tton of the ganghomc cham; g, the cerebral ganglia. The following common characters of the Arachnida, how· ever, help out our diagnosis .in practice. They ueve( possess more than four pairs of locon1otive limbs, and the somites of the abdomen, even when the latter is well developed, are not provided with limbs. Again, in the higher Arachnida (Fig. 26), as in the higher Crustacea, the body is composed of twenty somites, six of which are allotted to the head ; but, in the former class, one of the two normal pairs of antennro is never developed, and the eyes are always sessile, while, in the highest Crustacea, the eyes are mounted upon moveable peduncles, and both pain; of antennro are developed. 'l'llE MYRIAPODA. 55 Fig. 27. B Fig. 2: .. -Anterior part of the body of S?olopendra llopei (after rewport).-A, .Anterior pa1 ~ of the body from above; B, from bdow; A, head proper; n, anterior thoracic · ~m1tes .i a, antennro ; C, antennre, labrum, and mandibles (Iv') from below· D under VIew of heatl, with the two pairs of maxillre (v' VI') covering the foregoing: ' The M YRIAPODA (Fig. 27) have the chitinous integum nt; the body divided into somite , provided with articulated appendages; and nervous an l circulatory rgans con tructed upo~ a similar plan to those of the former groups. The body consmts of more than twenty somite , and tho c which corr·e-pond with the abdom n of Arachnida are provided with locomotive limbs. The head consists of at least five, and probably of ix, coale cent and modified somites, and some of the anterior segment of the body are, in many genera, coalescent, and have their appendages pecially modified to subserve prehension. rrh respiratory organs are trachem, whieh open Ly stigmata upon the surface of the body, and the walls of which arc strengthened by chitin, so disposed as readily to pull out into a ·pirally coiled filameut. The lNSE TA, lastly, have re piratory organs like thos of th My'riapoda, with n nervou and a circulatory syst m dis- |