TRÄGARDH, MORPHOLOGY AND PHYLOGEN!^ OF PARASITID^. 11 



the female (Fig. 17) the 3 posterior ones are considerably longer 

 and stouter, pectinate and curved downwards and backwards, 

 so as to meet the acute point of the epigynial shield. In the 

 male, on the contrary (Fig. 18), only the hindmost pair is 

 bipectinate at the base; the others are slender and weak. 



This difference seems to indicate, that in the female the 

 hairs have some function at the coition, and it is probable 

 that together with the pointed top of the epigynial shield 

 they hold fast the spermatophorous sac. 



In this connection it is of special interest to observe that 

 in most of the genera, in which the J^ genital aperture has 

 a posterior position, in the females the epigynial shield is 

 comparatively much larger than in the others, besides pro- 

 jecting so far forward that the top of ten projects beyond 

 the posterior margin of the gnathosoma. 



The mandibles of these males, on the other hand, show 

 no secondary adaptations; and from this we may conclude 

 that they have no function to perform at the coition. Hence 

 there has been no necessity for the J^ genital aperture to 

 move forwards to the anterior edge of the sternal shield. 



On the peritremata. 



The peri trema is a structure very characteristic for the 

 Parasitidce, although a homologuous structure seems to exist 

 in some Ixodidce, where there appears to be a short, super- 

 ficial groove in the so called stigmal plate. It is possible to 

 discern at least 3 main types of peritremata in the Parasi- 

 tidce, with no strict limits between them, besides which there 

 are a few genera in which they are entirely missing. These 

 are Greeniella, Epicrius and Iphis. The 3 types are the fol- 

 lowing: the extremely short one, the long, more or less straight 

 type, and the long undulated type. 



The short type occurs in some Liponyssus, in Spintiirnix, 

 Ptilo7iyssus and Zercon (Fig. 19). 



The long, undulated type occurs in the Uropodince 

 (Fig. 20) and the long, more or less straight type occurs in 

 the main part of the group (Fig. 21). 



I have not found that any authors have dwelled upon 



