420 



ZOOLOGY 



Pia. 2iO.—Cheyletus flabellifer 

 (Book Mite, quite iinconuected 

 with 'books). 



The alimentary canal is often provided with salivary 

 glands ; the stomach may give off numerous caeca, which in 



some cases are forked. The stig- 

 mata are two in number, situated 

 near the hind pair of legs, the 

 tracheae may be long and fine, in- 

 terlacing with the viscera, but in 

 some species {Nothrus) they are 

 short and thick, and in Hoplophora 

 they are still shorter and end in 

 swollen vesicles. 



As a rule a circulatory system is 

 absent, but the Gamasidae, or beetle 

 mites, are described as having a two- 

 chambered heart with two pairs of 

 ostia. 



A coxal gland has been de- 

 scribed, but no opening to the exterior has yet been found. 

 The nervous system is very concentrated, one or two pairs of 

 eyes may be present or these organs may be entirely absent. 



The male and female generative glands are very much alike ; 

 as in Phalangids, they form a ring. Their external opening is 

 on the anterior end of the abdomen or between the last pair of 

 legs. The Acarina are oviparous, the young are hatched with 

 three pairs of legs and undergo a num- 

 ber of ecdyses. Splmerogyna venfricosa 

 is said to give birth to mature mites 

 which are fertilised as soon as born. 



The Acarina are divided into many 

 families, some of which may be men- 

 tioned. The Deematophili comprise 

 one genus, Demodex, which is found 

 living in hair follicles both in domesti- 

 cated animals and in man. It has a 

 suctorial rostrum, four pairs of rudi- 

 mentary legs, and a long annulated 

 abdomen. 



The Saecoptidae are microscopic mites which live parasitic- 

 ally in the skins of mammals, and give rise to diseases known 



Fig. 241. — Demodex foUi- 

 culorwm, Simon. Under side. 



Eudimentary legs. 

 Abdomen. 



