THE ACAEINA OR MITES. 



73 



of these organs is not fully known, but the sacculus contains spermatocysts which are 

 supposed to reach it through the annulate tubes. 



Some, if not all, of the Parasitidae have a most remarkable method of coition, which 

 Michael has discovered and described in detail. The male, which is commonly a 

 little smaller than the female, clasps the latter by the legs of one side and crawls under 

 her. His abdomen extends back beyond that of the fe- 

 male, and he grasps her with his legs. Then a clear sac 

 emerges from the genital aperture of the male, gradually 

 enlarging until it is of full size and shape, which is constant 

 for each species. Usually this sac or bubble is flask-shaped, 

 with a long neck. It incloses the spermatozoa floating in a 

 clear viscid liquid (sometimes within spermatocysts). The 

 male clasps this bubble with his mandibles, which are 

 often modified apparently for such purpose. The male 

 then applies the small end of the bubble to the vulva of 

 the female, often inserting his mandibles for some distance. 

 Here the small end of the bubble bursts and the liquid 

 and spermatozoa are discharged into the spermatheca of 

 the female. The bubble is rather firm, and when empty 

 does not collapse, but shrinks somewhat. After the male 

 leaves the female he proceeds to clean his mandibles. In 

 those species in which the female has no spermatheca, 

 but has annulate tubes connecting to the acetabula of the 

 third pair of legs, it is probable that the bubble is ap- 

 plied to these apertures and not to the vulva, the sperma- 

 tozoa thus passing into the sacculus fsemineus, from which 

 they may pass into the ovary as occasion demands. In 

 the male of one species there is a hole in the jaw, through 

 which the bubble is pushed, part hanging on either side. 



Trouessart has claimed that in Raillietia there is a true parthenogenesis; agamic 

 generations are found in spring and summer, the male appearing only in the autumn 

 or winter. But he may be mistaken, as some other cases of alleged parthenogenesis 

 have been disproved by subsequent investigations. 



Parasitids deposit eggs which hatch into pale, 

 soft-skinned, six-legged larvae, often very dif- 

 ferent from the adult. There is a remarkable 

 exception in Pteroptus and alUed genera of the 

 Dermanyssinae, the young of which hatch ^\^th 

 eight legs. Normally the larva molts into an 

 eight-legged nymph. In this stage they have 

 shields, the dorsal often transversely divided. 

 The nymphal stage is often the longest and 

 most active period of their life — the stage of 

 growth and development. After one or two 

 molts in this stage some forms approximate 

 closely in appearance to the adult condition. 



Berlese considered that in this family, or at 

 least in certain species, there are several more 

 developmental stages than in other mites. The series included larva, protonympha, 

 nympha, deutonympha, tritonympha, nympha generans, nympha coleoptratae, and 

 adult. Michael has shown that this is wrong, and that there are only the larva, 

 protonympha, deutonympha, and adult. The larva is known by having but six 

 legs; the protonymph by having ? very short peritreme; the deutonymph by hav- 

 ing a longer peritreme, and the adiilts by the development of the genital aper- 



FiG. 139.— Periglischrus jher- 

 ingi: Female. (Original.) 



Fig. 140. — Sternostomum rhinolethrum 

 ( Original. ) 



