ORDER ACARINA: THE MITES 



291 



ending in a claw and often a sucker ; in the first two pairs of 

 legs there is usually a clubbed hair near the base of the tarsi, 

 and a very long hair near the base of the preceding joint. 

 These mites eat almost anything, and often do great damage 

 to dried provisions, flour, grain and other seeds, drugs, hay, 

 museum specimens, entomological collections, etc. They 

 multiply very rapidly. The larva has three pairs of legs, 

 and either proceeds by successive moults, in the ordinary 

 way, to the adult stage ; or may, after reaching the eight- 

 legged nymph stage, transform into a quiescent Hypopus 

 stage in which it emigrates abroad by affixing itself to some 



Fia. 128. — Female Itch-mite, ventral view. 



Fio. 129. — Female Sugar-mite, 

 ventral view. 



actively locomotive insect, this being effected by a patch of 

 suckers situated at the hind end of its body on the ventral 

 surface. 



The Hypopus, which is exceedingly minute, has a hard 

 chitinous integument and stumpy legs: it does not feed, 

 having the piouth and its appendages quite vestigial. When 

 it has been carried to some suitable locality, distant from its 

 overpopulated birthplace, it again transforms at a moult into 

 a nymph and resumes the even tenour of its development. 

 The " Hypopus question " furnished abundant material for 

 speculation, until Michael showed by experiment that it is 

 an ordinary alternative developmental stage favourable to 

 the spread of the species by emigration. 



