18 ARKIV FÖR ZOOLOGI. BAND 7. NIO 12. 



of the H eterozercon- or of Discomegistus-tyipe. — which differ 

 widely from one another — remains an open question. 



There is no statement of a »tarso curtissimo» in Disco- 

 zercon, and from tbis we may feel justified in assuming that 

 there is no distinct telotarsus on legs I. 



The shape of H eterozercon is ' elongate, oval, length to 

 width being as 4: 3 (according to Berlese's drawing); in 

 Discozercon it is very broadly oval, length to width being as 

 4,7:4,2, in Discomegistus it is considerably wider than long 

 (length to width as 2:3). 



Remains the most remarkable character, the ventral discs. 



In H eterozercon they are very small, compared with the 

 size they attain in the otlier genus, not being larger than 

 the coxse, while in Discozercon they occupy nearly the entire 

 space between coxae IV, the postero-lateral and the posterior 

 margin of the body. 



The structure seems also to be entirely different. Berlese 

 describes the discs of H eterozercon as follows: >>Ad latera an i, 

 scutuli punctulati duo conspiciuntur, ovales, foramine ovali 

 perforati, quod foramen occludere videtur operculus trunco* 

 conicus, mobihs (quod cum musculis quibusdum communicet) 

 organum totum valde discuhs sarcoptidarum, simile; sed veram 

 naturam eius ignoro». On examining the accompanying figure 

 [fig. ] b, Pl. 9], to which, however, no explanatory notes are 

 appended. we notice that the punctured plate is surrounded 

 by a narrow marginal plate, not punctured, which has one 

 external and one median projecting angle, on each of which 

 a hair is inserted. The shield is covered by a smaller, oval, 

 transversal plate, which is contiguous to the anterior edge 

 of the marginal plate. To the middle of this there seems to 

 be hinged as a lid another plate, of a truncated conical form, 

 which would be the plate B. believes to be moveable, as there 

 are muscles attached to it (to its base?); covered by the hd 

 there would be an opening, if the above interpretation is true. 



A feature which seems to be of importance in connection 

 with an attempt to homologize this organ is that it has no 

 relation whatever to the metapodial shields. 



If we compare these discs with those of Discomegistus, it 

 becomes evident that they have nothing in common, 

 except the position behind coxae IV and their pro- 

 bable function of adhering organs. 



