1922] Ewing: Phylogeny of Gall Mites ' 219 



taking place in the genus Paratetranychus , has taken place 

 in genera Tetranychus and Oligonychus; while in another genus 

 in the same family, the genus Anychus, both claws are gone. 



Thus it is seen that not only is the Eriophyid tarsus struc- 

 turally more nearly related to a type found in the Tetranychidae, 

 but it can be homologized with the latter type, and the evolu- 

 tionary changes necessary to give the exact Eriophyid tarsus 

 are actually observed now in progress in the group from which 

 we would derive the Eriophyids. 



THE FORM OF THE BODY IN THE ERIOPHYID/E AND 

 THE TETRANYCHID^. 



Next in morphological importance to the structure of the 

 mouth-parts and of the tarsal armature and number of legs 

 in the Eriophyidae, is probably the form of the body. It is in 

 nearly all species vermiform, in fact one of the common names 

 of the suborder of gall mites is Vermiformia. In addition, 

 the long-drawn-out body is ringed with many circular folds 

 of the integument. 



This ringed, vermiform condition is only matched in the 

 hair follicle mites of all the other major mite groups, and the 

 hair follicle mites are so different from the gall mites in 

 practically all other respects that a suggestion of their affinity 

 with the Eriophyidae has never even been made. 



Undoubtedly the vermiform body of a hair follicle mite is 

 an adaptation — an absolutely necessary adaptation — to its 

 life in the hair follicles, and with almost complete assurance 

 we can accept it that their origin and descent is from some 

 ectoparasitic zoophagous group, probably from the parasitic 

 Cheyletidse as held by Hirst. 



Searching elsewhere in the different groups of the Acarina, 

 instances of a vermiform tendency are found in several of them 

 and as has been noted, exists in the Tarsonemidas, more par- 

 ticularly, however, in the female, for the males of the Tarsone- 

 mids are as a rule short-bodied. In the Tetranychidae we find 

 not only examples of this tendency to develop the vermiform 

 type of body, but it is correlated with the development of 

 the gall-producing habit. 



In such free-living and active genera as Tetranychus and 

 Paratetranychus the body is stout, but in other, genera where 

 the attacks of the mites are so restricted that they live almost 



