TRÄGÅRDH, MORPHOLOGY AND PHYLOGENY OF PARASITIDiE. 3 



by a narrow strip of soft cuticle (Figs. 1 and 2). In other 

 genera the adults have a single dorsal shield, sometimes so 

 completely coalesced with the ventral shields that no traces 

 of the fusion, in the shape of sutures are visible (Figs. 3 

 and 4). In this direction the males are more pronounced 

 than the females, for the obvious reason, that in the latter 

 a fusion of the shields would be an obstacle to the increase 

 of the body accorapanying the ripening of the eggs. 



In most of the genera, where the adults have a single 

 dorsal shield, the nympha still have two (Fig. 5) and this 

 seems to be an obvious example of the biogenetie fundamen- 



K 



il '% 



u 





\ ' 



Fig. 3. 



Fig. 4. 



Fig. 5. 



Fig. 3. Parasitus armatus C. L. Koch. cT, dorsal view (after Trägårdh). 

 Fig. 4. Eulcelaps grahamensis Tgdh. $, dorsal shield X 60 (after Trägårdh). 

 Fig. 5. Parasitus fiicorum (DG) nympha, dorsal view X 21. 



tal law; and that the presence of 2 dorsal shields is a primi- 

 tive feature, still possessed by the more primitive genera, but 

 which has disappeared in the more recent, where only the 

 nymphae still possess this characteristic. 



There are, however, reasons which argue in favour of 

 the hypothesis of the primitive Parasitidce having possessed 

 more than two dorsal shields. 



As a matter of fact, there is at least one genus which 

 has more than two dorsal shields e. g. Sejiis K. In the fe- 

 male of S. togatus K. there are, between the anterior and 

 the posterior shield, two pairs of small, transversally oval 



