80 



PROCEEDINGS OF THE NATIONAL MUSEUM. 



VOL. XXVIII. 



Fig. 156.— Beak of 



HISTIOSTOM.V All ER- 

 IC. \N.\. 



that will induce a nymph to transfoi'm to a ITypopiis are not known. 

 ]Meg"nin supposed that the dryness of the air or the scarcity of food 

 were necessary causes. But Michael has shown that Jlypopl are 

 developed in the absence of these conditions, and tliat the Ili/j>02>>(s 

 is the natural and normal means of distributing the species. 



In the early days of the science of acarolog-y this connection was 

 uidcnown; therefore II[jpopu^ stood for a separate 

 g(-nus. allied more to (Jama.sns than to TyroglyphvH. 

 Dujardin in 1850 concluded that Hypopim was the 

 pupal stage of Gamasidte. As investigation proceeded 

 lIyp)opus was so frequently found in association with 

 Tyroglyj>hu8 that views were advanced as to their rela- 

 tionship. One was that Ilypxqjus was a ferocious 

 parasite devouring the Tyroglyp>hw< from within; 

 another, that Jlypopus was the male of Tyroglyphus, 

 and a third, that TIy])op\i8 was the real adult of cer- 

 tain species of Tyroglyphus. The " Hypopus ques- 

 tion" disturbed acarologists for a long time, but 

 throuo-h the work of Megnin and Michael it has been settled. In 

 some species of Glyclj>Jiagn8 the IIyj>oj>us is not fulh' developed and 

 does not escape from the n\"mphai skin. 



Most of the Tyroglyphidce differ Ijut little in general appearance, 

 and the characters that separate species are often few and minute. 

 The familv is usualh' considered to have affinity to the Sarcoptidaj and 

 Analgesidfe, but there is more resemblance to the nymphs of the 

 Oribatidte; in fact, Oribatid nymphs 

 have been described as Tyroglyph- 

 idtC, and r!c<' verKO. 



The Tyroglyphidje feed mostly on 

 vegetable matter; a few live on ani- 

 mal food. They are partial to stored 

 foods, and so are often of much eco- 

 nomic interest. A long list of arti- 

 cles attacked ))y them could be 

 compiled. It would include cheese, 



flour, hams, dried meats, hair in furniture, cereals, many drugs, dried 

 fruits, seeds of all kinds, bulbs, feathers, hay, and entomological spec- 

 imens. Their ravages are due to the enormous number of individuals 

 developed from a few in a short time. Materials attacked by them are 

 often in a few-days swarming with millions of the tiny creatures. " How 

 to get rid of them is often a di tiicult problem. Since they have no tracheaj, 

 they are not very susceptible to fumigation, although some of them will 

 succumb to such treatment. Flowers of sulphur and carbolic acid are, 

 at times, of much use. But in many cases destruction of the material 



fm\\nZ 



Fk; 



157. — Llii; I, AND TII- OF MANDIBLE OF 

 HISTIOSTO.MA A.MERICANA. 



