322 MANUAL OF ZOOLOGY. 



suckers, and the two posterior are terminated by bristles ; the 

 mouth, also, is furnished with bristles (fig. 165, C). In the 

 Ticks (Ixodes) the mouth is provided with a beak, or " rostrum," 

 which enables them to pierce the skin and retain their hold 

 firmly. In the Hydrachnidcs (fig. 164, c\ or Water-mites, the 

 head is furnished with two or four ocelli, and there are four 

 pairs of hairy natatory legs. They are parasitic, during at 

 least a portion of their existence, upon Water - beetles and 

 other aquatic insects. They pass through a metamorphosis, 

 the larva being hexapod, or having only three pairs of legs. 

 The Garden-mites (Trombidida) and Spider-mites (Ganasida) 

 live upon plants; the Wood-mites (Oribatida) and Harvest- 

 ticks (Leptidce) are to be found amongst moss and herbage, or 

 creeping upon trees or stones ; whilst the true Ticks (Ixodidce) 

 attach themselves parasitically by means of their suctorial 

 mouth to the bodies of various Mammals, such as sheep, oxen, 

 dogs, &c. Several Mites (Thalassarachna, Pontarachna, &c.) 

 have been found to inhabit salt water, and several species of 

 Trombidida live habitually between tide-marks. 



Another member of the Acarina is the curious little Demodex 

 folliculorum (fig. 165, A), which is found in the sebaceous 

 follicles of man, especially in the neighbourhood of the nose. 

 It is probable that very few, if any, individuals are exempt 

 from this harmless parasite. 



ORDER III. ADELARTHROSOMATA. The members of this 

 order, comprising the Harvest-spiders, the Book-scorpions, &c., 

 are distinguished from the preceding by the possession of an 

 abdomen, which is more or less distinctly segmented, but generally 

 exhibits no line of separation from the cephalothorax, the two 

 regions being of equal breadth and conjoined together. The mouth 

 is furnished with masticatory appendages, and respiration is 

 effected by trachece, which open on the lower surface of the body 

 by two or four stigmata. 



Family i. Phalangida. The well-known "Harvest-men" 

 belong to this family. They are characterised by the great 

 length of the legs (fig. 166, B), and by the filiform maxillary 

 palpi, terminated by simple hooks. The abdomen and cepha- 

 lothorax are of about equal width, but clearly marked off from 

 one another, and the former is segmented. There are two eyes, 

 and the young pass through no metamorphosis. The Harvest- 

 men are active in their habits and live upon animal food. 



Family 2. Pseudoscorpionidce (Cheliferidce}. The members 

 of this little group are readily recognised by the fact that the 

 maxillary palpi (fig. 166, A) are of large size, and are con- 

 verted into nipping-claws .or chelae, thus giving the animal the 



