NO. 10 II:EUING organs of AKACIIMDA — SNOIX^RASS 6/ 



hypostomc is a pair of ajijiendicular processes. In Opiliacarus scg- 

 uicntatns, as described by Witli, the outer process of each pair { :\, in) 

 is a toothed lobe articulated on the coxa, and is termed by With the 

 "maxillary lobe"; the inner one (/') is a thin lamella distinguished 

 as the "maxillary plate." The palps of the notostigmatid pedij)alps 

 are four-segmented beyond the coxa, and each bears a pair of prctarsal 

 claws. 



Proximal to the capitulum there j^rojecls from the ventral surface 

 of the body a median bifid process (fig. 23 E, t), which is apparently 

 a secondary development on the sternal region of the first-leg segment. 

 Some writers term this structure the "labium," but the similar ap- 

 pendage in Liamasides was designated a "liauchtaster" by Kramer 

 (1876), who showed it has nothing to do witii feeding, but probably 

 has some function in connection with mating, since the genital orifice 

 lies immediately behind it. 



Orihatoidca. — In the scheme of acarine classification the sarcopti- 

 form mites are not related to the Xotostigmata. but the sectional figure 

 bv Berlese (1897) of the capitulum of a species described as Orihates 

 globulus, probably Eucctcs scminuluin (O. F. Miillcr). given here at 

 A of figure 24, shows a remarkably generalized condition of the 

 mouth parts in combination with a well-developed capitulum. The 

 tectum (Tcct) is long and completely covers the retracted chelicerae 

 (Chi). The short, two-segmented chelicerae. however, are typical 

 chelate appendages, and, as shown in the figure, are merely invaginatcd 

 beneath the tectum, so that each is contained in a pocket of the head 

 wall inflected dorsally from the distal margin of the tectum, and 

 ventrally from the base of the epistome (Epst). The epistome and 

 ihe labrum (Lm) are together termed "labrum" by Berlese, but the 

 epistomal region is clearly identified as such by the attachment on it 

 of the dorsal pharyngeal muscles (did), while the labrum is the free 

 terminal lobe (Lnt) projecting over the mouth. The ventral wall of 

 the capitulum projects beyond the mouth (Mth), forming a short 

 under-lip structure, or hypostome (Hst), with a median sul>oral lobe 

 and a pair of lateral lobes. The pharynx (Fhy) is of the u.sual struc- 

 ture. If this is a true picture of the oribatid structure, the latter is 

 ty]iically arachnoid except for the presence of the long dorsal wall 

 oi the capitulum. which covers the chelicerae, and this feature is 

 merely an exaggeration of the structure in the Xotostigmata. 



Holothyroidca. — In this group, as in the Parasiti formes, the che- 

 licerae are elongate, deeply invaginatcd, and each is invested in a 

 specific tubular sheath. The capitulum of Hohlhynts hraucri (fig. 

 24 R), as described and figured by Thon (1006), is covered dorsally 



