72 



REPORT 108, U. S. DEPARTMENT OF AGRICULTURE. 



Fig. 137. — Spinturnix americanus. 

 (Author's illustration.) 



near the coxae of the third legs. The male genital aperture is usually at the anterior 

 margin of the sternal plate, only a short distance back of the mouth. In some groups, 

 notably the Uropodinse, the genital aperture of the male, or of both sexes, is situate 

 in the middle of the sternal plate. The anal opening is small and placed near the 



tip of the venter; it is often surrounded by a plate. 

 There is a spiracle or breathing pore on each side of the 

 body, above and slightly in front of the fourth coxa. 

 It is surrounded by a chitinous ring, the peritreme, 

 which usually extends forward for a long distance, 

 often in a slightly sinuous line. The legs are of six 

 joints — coxa, trochanter, femur, patella, and tibia, 

 of subequal length, and a long tapering tarsus. In 

 some species there are indications of a di\-ision of the 

 tarsus. The tarsi terminate in two claws, and some- 

 times a sucker or ambulacrum. In several forms the 

 anterior legs are destitute of claws, and seem to act 

 more as antennae. In many species the males have 

 the second pair of legs enlarged and provided with 

 teeth and projections, and sometimes the hind legs are 

 also armed. 



Trag&rdh has investigated certain points in the mor- 

 phology of the Parasitidae. The sternal area normally has 

 five pairs of bristles, three on the sternal shield, one on the 

 metasternal plates, and one on the epigynal shield. If the 

 sternal plate has four pairs it is evidence that the metas- 

 ternal plates have coalesced with it. There are some- 

 times other small sternal plates near the base of the legs that do not bear bristles; 

 these are called endopodal shields. Trag&rdh also considers that the numerous 

 shields on the dorsum of Sejus indicate segmentation. He also refers to the 

 fact that in those genera in which the male genital aperture is situated in the 

 sternum there is no modification of the male mandibles for carrying the sperm sac. 



The internal anatomy of the Parasitidae has been 

 studied perhaps more than that of any other family. 1 1 

 differs in various ways from what may be called the typi- 

 cal acarid anatomy. Kramer has shown that in some 

 forms there is a tendinous framework in the middle of 

 the body, a sort of internal skeleton, to which are at- 

 tached many of the larger muscles. The male sexual 

 organs are usually on the common plan. There is, how- 

 ever, a large accessory gland lying between and beneath 

 the vasa deferentia. There is no intromittent organ, 

 and sometimes there are two testes. The female gen- 

 erative organs usually differ much from that in other 

 families. Often there is a .semiglobular or botryoidal 

 ovary, opening into one (sometimes two) oviducts, 

 that lead to the vagina; above the vagina is a domed 

 chamber, the spermatheca. At times there are two small glands that open into the 

 vagina. In many forms there is no spermatheca, in which case Michael has discov- 

 ered the existence of other organs of a most curious nature. Attached to the toj) of the 

 ovary arc two rather clavale arms, known as the lyrate organs; and above is a large 

 sac, the"sacculus femineus," connected at one end to the ovary and at the other 

 by two annulate tubes to the acetabula of the coxie of the third jiair of legs. After 

 the eggs are deposited the sacculus becomes very small. Sometimes it is wanting, 

 but the annulate tubes are present and coimect direct to the ovary. The significance 



Fig. 138.— VoDter oiSpinturnii. 

 (.\uthor"s illustration.) 



