23 
PARASITIC MITES. 
Since but little is generally known of the nature and structure of 
inites, a brief account of their habits and a detailed description of the 
anatomy of the mite {Lelaps ecliidninus) wliich is concerned in the 
transmission of H. perniciosum is given below. 
The Acarina, an important group of the Arachnida, comprise the 
mites and ticks, the former being greatly in the majority as regards 
number of species. The term ^Anites” is often applied to the entire 
group of Acarina. In addition to their arachnid characteristics (the 
absence of anteim^e and the possession of four pairs of legs) the 
Acarina are distinguished by the absence of a division into thorax 
and abdomen, and by the arrangement and structure of the mouth 
parts, which are adapted for puncturing and sucking. The larva 
resembles the parent except in the possession of three pairs of legs 
and the absence of sexual organs. After casting the skin two or more 
times (ecdysis) the adult stage, vdth four pairs of legs and fully formed 
sexual organs, is attained. 
Canestrini’s® classification, from a scheme devised by Kraemer, 
divides the Acarina into six subheads: 
Astigmata (Sarcoptic and vermiform mites). 
Hydra Carina CWater mites). 
Prostigmata (Harvest mites). 
Ci'j’ptostigmata (Orl)atid mites). 
Metastigmata (Ticks). 
Mesostigmata (Gamasid mites). 
A number of classifications varying in slight degree have been 
based upon this original. The following classification of the Acarina 
is from Xeumann: ^ 
Nonve r- 
mifo rm 
Acarina- 
Legs inserted directly 
into the integument 
without epimerae ■ 
Legs articulated on dis- 
tinct epimerte 
V e r m i -1 
form! 
AcarinaJ 
Legs with five articles . . 
Tegs with three articles 
Legs with five articles Oribatidae, 
{( Provided with 
booklets Ixodidas. 
Didactylous or 
styliform Ga masidse. 
With no tracheae (marine 
forms) Halacaridx. 
Natatorial legs (aquatic) HydracTinidse. 
Chelicerae styliform; palps 
free, antenriiform BdelUdx. 
Chelicerae styliform or in 
Amlmlatory legs claws; palps' free, ravishers. . Trombididse. 
Chelicerae didactylous; palps 
cylindrical or conical and 
partially adherent to the 
tips Sarco ptidse. 
Phytoptidx. 
.Demodecidae. 
Of these ten families only five are parasitic — the Ixodidx (s. 1.), 
Gamasidse, Trombididse, Sarcoptidse, and Demodecidse. Many of these 
are commensals, obtaining nutriment from the organic detritus, 
« Canestrini, S.: Prospetto delT acarofauna Italiana., Padova, 1885-1897. 
^ Xeumann, L. G.: Traite des maladies parasitaires non microbiennes des animaux 
domestiques. TTansl. by Fleming. Ed. by J. McQueen. 2d ed. Xew TTork, 1906. 
