annulosa: arachnida. 241 



sitically by means of their suctorial mouth to the bodies of 

 various Mammals, such as sheep, oxen, dogs, &c. Several 

 M\X.s& {Thalassarachna, Fontarachna, &c.) have been found to 

 inhabit salt water, and several species of Trombididcs live habit- 

 ually between tide-marks. 



Another member of the Acarina is the curious little Demodex 

 foUiculorum, 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 harm- 

 less 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 trachese, which open on the lower 

 surface of the body by two or four stigmata. 



Family i. Fhalangidce.—'Th& well known "Harvest-spiders" 

 belong to this family. They are characterised by the great 

 length of the legs, and by the filiform maxillary palpi, termi- 

 nated by simple hooks. 



Family 2. Fseudoscorpionidm {Chehferidee). — The "Book- 

 scorpion " ( Chelifer) is a common little animal in old books. 

 It is distinguished by the fact that the maxillary palpi are of 

 large size, and are converted into nipping-claws or chelae, thus 

 giving the animal the appearance of a Scorpion in miniature. 



Family 3. Soipugidce. — In this family the abdomen is not 

 only very distinctly segmented, but is also clearly separated 

 from the abdomen. The mandibles in Galeodes, which is the 

 type of the group, are chelate, but the maxillary palpi consti- 

 tute long feet. 



Division B. Pulmonaria. — Respiration by pulmonary sacs 

 alone, or by pulmonary sacs conjoined with trachea. Fyes six 

 or more in number. Abdomen usually distinct from the cephalo- 

 thorax. 



This division comprises the higher Arachnida, such as the 

 Scorpions, and the majority of what are commonly known as 

 Spiders; the former constituting the order of the Fedipalpi, 

 the latter that of the Araneida or Dimerosomata. 



Order I. Pedipalpi. — In this order are the true Scorpions, 

 together with certain other animals which are in some respects 

 inteiTOediate between the Scorpions and the true Spiders. 

 The members of this order are distinguished by the fact that 



