BRITISH TYROGLYPHID7E. 



diidse, Hydrachnidae, Ixodidae, etc. ; nor liave they any 

 other known organs of special sense except the palpi, 

 which are far less highly developed than they are in 

 many other families ; the trophi are simple, the man- 

 dibles alone being highly developed ; these are usually 

 chelae working perpendicularly, which is the commonest 

 type among Acarina ; the maxillary lip still shows its 

 maxillary origin, although the maxillae are probably 

 not functional as such; the lingua is but slightly 

 developed, and there is not usually any epipharynx, 

 which is an important organ in Bdella and many other 

 Acari ; still most of the species are active creatures, 

 which do not seem to suffer at all from the want of 

 special sense organs or other deficiencies. 



Probably to the biologist the most interesting point 

 connected with the Tyroglyphidae will be found to be the 

 hypopial stage, which so greatly assists in the distribu- 

 tion and preservation of many of the species. This 

 stage, as far as we know, has not any exact parallel in 

 nature outside the Acarina ; even amongst them, with 

 one or two very doubtful exceptions, it is confined to 

 the Tyroglyphidae. A full account of this stage in the 

 life-history, and of the opinions which acarologists have 

 held concerning it from time to time, will be found in 

 the chapter of this book on development and the im- 

 mature stages. 



The popular idea of the Tyroglyphidae is based upon 

 the common cheese-mites, Tyroglyphus siro and T. 

 longior, of which the latter is found in even greater 

 profusion than the former ; they may properly be con- 

 sidered as fairly typical, and T. siro is most commonly 

 received as the type by acarologists as well as others. 

 It was one of Linnaeus' very few species of Acari ; but 

 that eminent naturalist evidently confused it with the 

 itch-mite ; as, indeed, the name siro shows ; but the itch- 

 mites are really very different creatures, not Tyrogly- 

 phidae at all, and considerable confusion has thus arisen. 

 The species which we now call T. siro, whether it be 

 Linnaeus' original species or not, is well defined ; pro- 



