NO. 1382. 



THE ACARINA OR MITES— BANKS. 



79 



before the tip; it i.s often but an elongate slit, with a suckinii--disk 

 each .side. In GIycij)hagus the opening-.s are much larger, and the 

 genital sometimes occupies the entire area between the coxse. 



The internal anatomy of the Tyroglyphidfe has been carefully 

 studied by Nalepa and Michael. The digestive system is of the usual 

 type; the ventriculus is very large, with two short cceca, the colon is 

 globose, the rectum very large, and opens close to tip of body. 

 Behind the anus is a small opening — the copulative aperture. In 

 Gh/eiphagufi the bursa copulatrix projects externally in a small cone. 

 So in the Tyroglyphida\ as in the Analgesida% copulation is not per- 

 formed through the vulva, but by this special opening. This opening 

 leads to a receptaculum seminis, which 

 connects by a small duct to the ovaries. 

 The nervous system is chiefly concentrated 

 in the very large "" brain " which surrounds 

 the oesophagus. The most powerful mus- 

 cles of the mite are those attached to the 

 mandibles, the legs, and the stomach. 



As a rule there is little difference in 

 size between the sexes, but Michael has 

 described one form with the male not half 

 as large as the female. In several cases 

 there are well-marked secondary sexual 

 characters, such as the enlargment of the 

 first or third pair of legs in the male. 



The transforn)ations of the Tyroglyph- 

 id;e are among the most marvelous of the 

 animal kingdom. All Tja'oglyphida? 

 (except CarpogJi/pJnis) appear to la}^ eggs, 

 sometimes of large size. The young on 

 hatching are six-legged, and, molting, 



obtain two more. Thenceforward their life-historv may take the 

 simple and direct path to the adult condition, but often it passes 

 through what is called a IIyj)oj)u.i^. This Ilypopnx: is ver}" different 

 from the creature from which it has developed — the octopod nymph. 

 Its bod}" is hard and chitinous; there is no mouth-orifice and no dis- 

 tinct mouth-parts. The legs are short and ill adapted to walking. 

 On the ventral surface of the body near the tip is an area distinct 

 from the general surface and provided with several circular marks or 

 sucking disks. By means of these sucking disks the Hypopus attaches 

 itself to an insect or other creature and is transported to some other 

 locality, where it may find a suitable breeding place. The IIy]?opus is 

 thus a stage in the life of TyroglypJmi^ for the purpose of migration. 

 The IIyj)(>jJi<.s, on finding a suitable locality, molts into an octopod 

 nymph, which will feed and develop into an adult mite. The causes 



Fig. l.'i.'i. — HisTiosTOiM.i amekh.'ana. 



