TRÄGÅRDH, MORPHOLOGY AND PHYLOGENY OF PARASITIDiE. 21 



In my opinion \ve are obliged to assume that the sternal 

 and metasternal shields are nothing but coxal plates. 



It is now a definitely proved fact.. amongst other things 

 by With's and Reuter's researches [12. p. 40—41; 18. p. 

 150] that those which originally were, and still are free joints 

 articulated to the body in many groups, for example in Trom- 

 bidiince, Eupodince amongst others, have successively coalesced 

 with the ventral surface, at first as distinct plates, the so- 

 called epimera {Hydrachnidce), t hen final ly entirely fused with 

 the ventral side. 



This gradual transformation of the coxse being actually 

 proved in other groups, there is nothing preposterous in the 

 assumption of the same regressive development having taken 

 place in the Parasitidce. 



If the above interpretation be triie, then the present 

 name of the shields ought to be changed, since they convey 

 the false idea that the shields are veritable sterna, and the 

 name syncoxal plate instead of the sternal, and inetacoxal in- 

 stead of the metasternal plate, would perhaps be more ap- 

 propriate. 



On the phylogeny. 



From the above researches it follows, that with regards 

 to the position of the male genital aperture the U ropodince. 

 and the Zerconince are more primitive than the other sub- 

 families. In other respects however the Uropodince are highly 

 specialized. In connection with their lichenivorous and ligni- 

 vorous habits and with these correlated sluggish movements, 

 their passive defensorial organs have acquired a high degree 

 of perfection which contends successfully with the biological 

 type represented by the Chelonia to which they bear a strik- 

 ing analogy. 



Thus they are apt to conceal perfectly their gnathosoma 

 between the top of the dorsal shield and coxse I, which are 

 very large and can he locked one with another; the legs can 

 be retracted in the foveolae pedales and partly protected by 

 thin, horizontal lamina partly by the thin ventral blades of 

 the joints which cover one another when the legs are in their 



