Ewing — Significance of Parasitism in Acarina. 9 



typical of several of the well-known groups of mites, the 

 chelate chelicerae being the most common type in the 

 Acarina. The most curious fact in regard to this genus^ 

 the phylogenetic significance of which is much in doubt, is 

 the possession of four dorsal stigmata. This character is 

 so different from that of any of the other known Acarina 

 that the genus has been raised to the rank of a suborder 

 by some acarologists. 



The Eange of Paeasitism in the Acarina. 



In order to determine the origin and significance of 

 parasitism in the Acarina it is necessary to study the 

 range of parasitism within the order, to determine the 

 relationships between the parasitic and the free-living 

 forms. 



This study can only be tentative at this time ; for only 

 a small proportion of the acarid fauna of the world is 

 known. The results of such a study are shown in tab- 

 ular form below, and in the further notes regarding sep- 

 arate families that follow the table. 



