NO. 10 FEEDING OKCANS OF AKACllNIUA — SNOIXJRASS 65 



say only that it may be so, but tliat developinental evidence would be- 

 more convincing. 



The mouth parts of the .\carina differ structurally from those of 

 other Arachnida in no essential respect, as Borner (1902) has clearly 

 shown. Recent writers, however, make no effort to correlate the 

 acarine structure with that of arachnids in general, and their special 

 tirminologies become highly confusing: but, as Borner has said, since 

 tlic mouth parts of the Acarina agree perfectly with those of other 

 Arachnida. there is no need for the introduction of special terms for 

 structures that already have generally applicable names. The review 

 of the works of other writers that follows will show that the structural 

 facts are fairly well known in several important acarine groups. The 

 l)rescni writer has made no extensive study of the feeding organs of 

 the Acarina, and. therefore, will attempt merely to bring the various 

 jjublished accoinits together uufkr a uniform terminology based on a 

 concept of structural unity l)elwetn the Acarina and other Arachnida. 

 The terms used in the following descri|)tions may hence seem strange 

 to acarologists, but few will deny the desiral)ility of nomenclatural 

 reform. 



The only features of the acarine mouth parts that cannot be homolo- 

 gized with structures generally present in other .\rachnida are the 

 variously developed appendicular lobes or processes often associated 

 with the distal part of the hypostome ; lobes that are at least analogous 

 with them, however, occur in the Chelonethida (^fig. 12 A). These 

 accessory hypostomal processes of the Acarina afford useful characters 

 for specific descriptions, but each taxonomic writer usually has names 

 of his own for them, or no names at all. and no attemjjt will be made 

 here to invent a uniform terminology. The structures in question are 

 evidently secondary lateral outgrowths of the coxal processes that are 

 united in the hypostome : they are hence not "maxillary" processes, 

 though in their various designations the maxillary idea seems to 

 predominate. The structures might be called simply hypostomal proc- 

 esses. L'sually. when present, there is a pair of them on each side, 

 one member of which is lateral, the other mesal. 



Xotostigwata. — The capitulum and the mouth parts in this arachnid 

 group, as described by With ( 1904). while in no sense primitive, show 

 unquestionably an early stage in the evolution of the acarine capitulum. 

 The tectum, termed "ro.strum" by With, is a mere fold of the dorsal 

 integument over the bases of the chelicerae (fig. 23 A, K, Tcct), but 

 it is united laterally with the high basal angles of the i)edipalp coxae 

 (A, IICx), and thus forms the dorsal wall of a primitive capitulum. 

 From beneath the tectum project the large, fidly exjxjscd. three- 



