8 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxvin. 



deposited by the female. Ot'teu within this eg-g-, while the embryo is 

 developing, an inner membrane is formed which incloses the young 

 mite; this stage is the '' deutovum/' The outer shell may be cracked 

 so as to show this membrane, or it may be wholly discarded. The 

 larva at birth has ])ut six legs. It feeds for awhile, then passes into a 

 resting stage which in time discloses the eight-legged nymph. The 

 added pair of legs is the fourth, at least usually. During the nymphal 

 period tlie mite may molt one or more times and change its appear- 

 ance, but is always destitute of true genital orifices. At the end of 

 the lumiphal stage it passes again into a (piiescent condition, and in 

 due time molts into the adult mite. During these resting stages 

 nuich of the internal anatomy of the mite may undergo histolysis, 

 each new stage l)eing' rebuilt from the disintegrated tissues of the 

 preceding- stage. The genital organs are, however, not atfected by 

 these histolytic processes. 



The conmion impression that most mites are parasitic is entirely 

 erroneous. About half of the known species are not parasitic in any 

 stag'e, and manj' which are found attached to insects and other animals 

 are not true parasites thereon. Most mites 

 ordinarily move quite slowly, but when dis- 

 turbed some can travel at an astonishing pace. 

 A very few species are fitted for leaping. 

 Aquatic mites occur in ])oth fresh and sea water. 

 Ticks occur on mammals, l)irds, and even on 

 snakes and turtles. The bird-mites live on the 

 Fig. 6.-EMBKY0 of gamasus. feathers and skin of l)irds; the itch-mites bur- 

 row within the skin of man and other mam- 

 mals. Other species live in the cellular tissue of birds; a few occur 

 in the tracheal passages of seals, and one has l)een found living within 

 the lungs of a moid^ey. Many species feed on living plants, and the 

 gall-mites produce curious deformations on leaves and twigs. 



Mites are distriltuted throughout the globe, but appear to be most 

 numerous in temperate regions. Many are abundant in high latitudes. 

 Single species are sometimes widely distril)uted; however, as a whole, 

 mites are su))ject to the usual rules of geographic limitation. Most of 

 the parasitic forms follow the distril^ution of the host. A few of the 

 free mites are common in widely separated regions, but many, 

 especially the myrmecophilous ones, are very local. ]\Iost of the 

 free-living species and those parasitic on plants spread h\ their own 

 wanderings, but many have developed, for the purpose of migration, 

 a peculiar nymphal form (the ////ywy>^As), Avhich clings to other animals 

 that will visit places similar to the mite's birthplace. Most mites are 

 not readily destroyed l)y cold or moisture, and through this hardiness 

 can extend their distriljiition. 



Most mites have l)ut few enemies outside of their predatory relatives. 



