4 ARKIV FÖR ZOOLOGI. BAND 7. N:0 28. 



plates (Fig. 6) and the nymphse possess the same feature, 

 whereas in the male these are fused with the posterior shield. 



Thus the male has reached the degree of fusion of the 

 shields which in other genera the nymphse and females ex- 

 hibit. 



The assumption that in Sejus the great number of 

 dorsal shields is a primitive feature, and not a recently ac- 

 quired one, is borne out by some data with which the onto- 

 geny of some other genera furnishes iis. 



Fig. 6. 



Fig. 7. 



Fig. 7. 



Fig. 6. Sejus togatus K. ?, dorsal view X 50. 

 Liponyssus chelophorus Oudms. deutonympha. Dorsal view X 

 (after Oitdemans). 



Thus, the deutonympha of Liponyssus musculi K. has, 

 according to Oudemans [8. fig. 19, pl. 8] two pairs of small 

 shields between the anterior and posterior shield, which, as 

 regards their position, completely correspond to those of 

 Sejus; and in the nympha of Liponyssus chelophorus Oudms. 

 there are no less than 3 pairs of such small shields [8. fig. 

 27, pl. 9]. (Fig. 7). 



