1922] Ewing: Phylogeny of Gall Mites 217 



to the view of the present writer this opening is no other than 

 the mouth-opening which leads to the pharynx. 



So nearly alike are the mouth-parts of Phytoptipalpus 

 and those of the Eriophyidas, that to explain their complete 

 homology it is only necessary to point out their few differences. 

 The maxillae and the maxillary palpi are practically the same 

 in both cases except in Phytoptipalpus only a single fused 

 palpal segment is distinguishable, while in the Eriophyidas 

 three are usually recognizable. The stylets of the cheliceras 

 of the two groups are the same, except that in Phytoptipalpus 

 they are elbowed near the base. In Phytoptipalpus and all 

 of the spider mites the bases of the chelicerae are lodged in a 

 flat chitinous structure which may be in certain species 



Fig. 2. Ventral view of anterior part of body of Eriophyes pyri; 

 greatly enlarged. 



protrusible. This structure has long been known as the 

 mandibular plate. In working on the homologies of the 

 mouth-parts of the ErJophyidse the writer has found that in 

 E. pyri that the chelicerae both arise from a common base, 

 and that this base could logically be regarded as the same 

 structure which in the Tetranychidas and in Phytoptipalpus 

 is called the mandibular plate. It is a greatly reduced structure 

 in the Eriophyidas and in fact is vestigial. 



The pharynx and oral opening in the two groups of mites 

 are, as I have found, identical, although Tragardh regarded 

 the ventral opening in paradoxus as being a provision for the 

 thrusting out of the chelicerae. 



