Elementary text-book of zoology (1884) Elementary text-book of zoology elementarytextbo0101clau Year: 1884 400 ARACHNIDA. fused with the thorax. The oral apparatus is adapted for biting or piercing and sticking,. Respiration, as a rule, by means of tracheae. The body of the Acarina is generally small and possesses a stout and unsegmented form. The head, thorax, and abdomen are fused into a common mass (tig. 379). The form of the oral apparatus varies exceedingly, and may be adapted either for biting or for piercing and sucking. The chelicerse are accordingly some- times retractile styles, and
Elementary text-book of zoology (1884) Elementary text-book of zoology elementarytextbo0101clau Year: 1884 400 ARACHNIDA. fused with the thorax. The oral apparatus is adapted for biting or piercing and sticking,. Respiration, as a rule, by means of tracheae. The body of the Acarina is generally small and possesses a stout and unsegmented form. The head, thorax, and abdomen are fused into a common mass (tig. 379). The form of the oral apparatus varies exceedingly, and may be adapted either for biting or for piercing and sucking. The chelicerse are accordingly some- times retractile styles, and are sometimes furnished with claws or chehe. In the first case, the bases of the pedipalpi form a sheath which surrounds the styliform chelicera? and serves as a suctorial rostrum, while the peripheral part of the pedipalpus or palp frequently projects laterally, and ends with a claw or chela. The structure of the four pairs of legs is not less various, in- asmuch as they may serve for crawling, attachment, running and swimming. They usiially end with two claws, sometimes in parasitic forms with stalked suctorial discs. The nervous system is re- duced to a common ganglionic mass representing the brain and ventral cord. Eyes may be absent or may be present, as one or two pairs of simple eyes. The alimentary canal is frequently provided with sali- vary glands, and gives off on either side a number of blind saccular diverticula which may be forked (fig. 380). Heart and blood vessels are invariably absent, but respiratory organs are frequently present in the form of trachea?, which arise D PIG. 380—Anatomy of Ijcodea Ricinus (after Al. Pagenstecher). G, Brain; SpD, salivary gland ; Dff, ducts of salivary gland ; D, diverticula of intestine ; A, anus ; N, urinary organ ; Tr, 'bundles of trachea?; St. stigma. 3s Acariens en general et les families des Trombidies, Hydracbnes en mi. SV-. Xat., II. Ser., Tom. I. and II. H. Nicolet. ' Histoire 1'ovdre des part,' Ann. naturclle des
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