TWO SPECIES OE PARASITIC MITES. 335 



it, but in copulation it is turned backwards, when, of course, the 

 episternum is also turned back beneath it. 



The external sexual organ of the adult female is simply a narrow 

 slit running across the under surface of the body, about half way 

 between the insertions of the second and third pairs of legs. It is 

 rather an interesting fact, however, that the male does not copulate 

 with the fully developed female, but with the female in what has 

 been called the nymph stage, when the ventral opening into the 

 oviduct has not yet appeared ; another ecdysis being necessary 

 before the adult form is assumed. I have not had the opportunity 

 of observing the mode of copulation, but there would appear to be 

 no doubt that the anus serves for the opening both of the intestine 

 and the vagina. Ftirstenberg, in his' comprehensive treatise on 

 " Die Kratzmilben," does not mention the opening in the middle of 

 the ventral surface, but in Sarcoptes scabiei figured the oviduct as 

 opening into a cloaea along with the intestine, evidently not 

 recognizing the fact that the oviduct and vagina opened at different 

 parts of the body. He also states that he saw a male and female in 

 copulation, and that the penis was inserted into the anal opening. 



In the closely allied family of the " Dermaleichidae " also, the 

 arrangement of the female sexual organs is essentially as follows : — 

 There is a post-anal opening leading by a duct into the Receptaculum 

 seminis, which opens into the oviduct, at one end of which the 

 ovaries are placed, and the oviduct opens on the middle of the 

 ventral surface. It appears very probable that an arrangement of 

 the parts similar to the above exists in the genus Sarcoptes. 



With the exception of the absence of a ventral sexual opening, 

 and the slightly more posterior position of the anus, the nymph is 

 very similar to the adult female. 



The larva is somewhat smaller than the nymph, and is only 

 provided with six legs, the hinder pair of which end in long bristles 

 as in the adult females. 



The egg is small, oval or somewhat ovate, and about half the 

 length of the adult female. 



We have adopted Fiirstenberg's name minor for this species 

 instead of cati, which had previously been given to it by Hering, as 

 the first is characteristic of the species itself (it being very small), 

 and not merely of its habitat, for though it was first found on the 

 oat, it has since been found on the rabbit and other animals. On 



