64 BRITISH TYROGLYPHID^]. 



The Anus in the Tyroglyphidae is usually a mere slit 

 at or near the posterior end of the abdomen ; it is ordi- 

 narily upon the under-side. It may, however, be partly 

 terminal, as in Histior/aMer and H&rwia; it may have 

 more or less chitinized labia, which are sometimes thin 

 plates lying against one another ; their posterior ends 

 may project beyond the hind margin of the abdomen, 

 as in Glycyphagus sciurinm. There are often a few short 

 hairs round the anus, and in the males of Tyrof/lu/thus, 

 tiistioga&teT) etc., there is a pair of conspicuous copu- 

 lative suckers, one on each side of the anus, which is 

 generally large and capable of passing solid dejecta. 



The external genital organs are described in the 

 portion of this chapter relative to the reproductive 

 system. 



Interned A iia lomy. 



The Alimentary Canal, PL A, figs. 15, and PL C, 

 figs. 13 and 8, 10. 



Dujardin was of opinion that the Acari did not 

 possess an alimentary canal at all, but that the food 

 passed into the general body cavity. The erroneous- 

 ness of this view, notwithstanding that author's keen 

 powers of observation, has long been known ; the 

 alimentary canal in the Acari is a thoroughly closed 

 system, quite cut off from the body cavity, except so 

 far as fluids, and possibly even crystals, may pass 

 through the walls of the canal itself to some limited 

 extent as a physiological process, in the manner indi- 

 cated in the portion of this chapter where the ven- 

 triculus is more especially dealt with. Some, by no 

 means inconsiderable, anomalies occur in the system in 

 such families as the Trombididse, Bdellidas, Hydrach- 

 nidae, etc., which present more or less one type of 

 canal ; which although naturally having a resemblance 

 to the canal of the Tyroglyphidoe in its broad general 

 character, yet differs widely from it in many important 



