1922] 



Ewing: Phytogeny of Gall Mites 



221 



can actually be traced out not only in other groups of mites, 

 but in the Tetranychid^ and the Phytoptipalpidae the two 

 families held to be the most nearly related to the Eriophyidae. 

 Lastly the morphological changes thus traced out are correlated 

 with changes in habits which give finally a high degree of 

 approximation between the hypothetical ancestral group and 

 the group whose origin is to be explained. 



Bdellidae Eupodidae CaecuLidae 



Trombidudae 



1" 



Hy-JpacarLna 

 Er^ythmeldae 



Anustidae 



P h vjtopti palpidae 



Kuid 



oph^ 



ae 



Fig. 5. A "tree" diagram illustrating the origin and relationships of the families 



of Prostigmata. 



The relationship and origin of the Eriophyidae is indicated in 

 the following diagram (Fig. 5). For sake of completeness the 

 relationships of other families of the order Prostigmata are also 

 shown according to the writer's interpretation. 



The same relationships can be shown in the form of a key 

 to the families of Prostigmata; not so clearly, yet some practical 

 advantage may be obtained in the key by enabling one to place 

 properly a given species to family. A key to the families of the 

 suborder Prostigmata is here given in the form of a new classifi- 

 cation. In this classification the mouth-parts are made, to 

 a large extent, the basis for family differentiation. 



