CLASSIFICATION OF ACARINA 567 



The stigmata or external openings for the tracheae are usually situated 

 on thickened plates of chitin, and may either be single or in pairs. 

 In most of the terrestrial and aquatic acarians the 



Qij j 



stigmata are situated at the sides of the body and can 



easily be recognized with a hand lens. In the majority of the permanently 



parasitic forms stigmata are wanting and respiration is carried on through 



the skin. In many mites each stigma has a curious forward prolongation 



of a tubular nature, which is known as the peritreme ; its function is 



unknown. 



In all the acarians the sexes are distinct. The males are as rule smaller 

 than the females and are often difficult to find; in many cases they never 



attach themselves to the host on which the female is 



.._,.. . Reproduction 



parasitic. The reproductive organs open on the ventral 



surface close to the mouth parts. The male opening (epiandrum) is as 

 a rule smaller than that of the female (epigynum), which is generally 

 a large slit guarded by flaps , or valves. Copulation is peculiar, as the 

 mouth parts of the male are made to serve the purpose of a copulatory 

 organ. They are, inserted into the genital opening of the female, and as 

 the bag of sperms (spermatophore) is passed out from the male sexual 

 opening it is pushed into the female orifice by the mouth parts. In the 

 case of the parasitic forms copulation may take place either on the host 

 or away from it, the male awaiting the replete female. There are various 

 secondary sexual differences to be noted, such as certain plates and 

 shields and the shape of the dorsal scutum. 



CLASSIFICATION 



The classification of the Acarina is at present in an unsatisfactory state, 

 as no common agreement has been reached by workers on this subject. 

 As has been set forth in the introductory chapter, Ray Lankester 

 divides the order Acarina into seven suborders according to the position 

 of the stigmata. The Metastigmata includes the Ixodidae or ticks and 

 the Gamasidae, and the latter together with three other suborders 

 contains the mites which are of interest in the present connection. 

 Of these the Prostigmata includes the Trombidiidae or Harvest mites, 

 the Astigmata, the Sarcoptidae or Itch mites, and the Vermiformia the 

 Demodicidae. Banks divides the order into several superfamilies, which 

 are again divided into numerous families and genera. Another classifi- 

 cation is that given by Neumann, which is here reproduced. This 

 authority recognizes ten families, which he groups as follows; 



