XO. 10 IKEDING ORGANS OF AKAcH NII^A — SNODT.RASS 79 



which fact possibly explains Douglas' statement that the "stylet" of 

 Dcrmaccntor audcrsoni is "tripartite and (juite short." 



Above the basal lobe of the labruni is a tlat pocket (figs. 27, 28 A, 

 Slv) covered dorsally by the lower walls of the cheliccral sheaths. 

 Into the inner end of this pocket open the ducts of the salivar)' glands 

 (fig. 2j, SlDct). The supralabial pocket thus serves as a salivarium, 

 or receptacle for the saliva ejected from the ducts. Christophers 

 (1906), however, regarded it as the "mouth cavity," and Nuttall. 

 Cooper, and Robinson (1908) called it the "buccal cavity," which 

 terminology has been followed by more recent writers. It is clear, 

 however, that the space in question has no relation to the mouth or 

 to the intake of food ; it is appropriately named by Samson (1909) the 

 "Speichelhohle." The closure of the food canal of the hypostome by 

 the labrum must exclude the saliva from direct entrance into the 

 mouth ; its only access to the food stream, then, would appear to be 

 at the open distal part of the hypostomal gutter. 



The flow of saliva from the salivarial pocket, according to Bertram 

 (^1939), is regulated by movements of the labrum ("tongue-like 

 process"). The lumen of this organ in Ormthodoros, Bertram says, 

 is a closed chamber, presumably filled with liquid, the posterior end 

 of which extends into the pharynx against the anterior part of the 

 dorsal wall of the latter, and therefore reacts to changes of pressure 

 within the pharynx. The decreased pressure of the expanding pharynx 

 contracts the labral chamber and deflates the labrum ; conversely, 

 contraction of the pharynx dilates the labrum. The alternate expan- 

 sion and contraction of the labrum is thus supposed to exert a sucking 

 action on the saliva entering the salivarium from the salivary ducts. 

 .\ similar mechanism has not been observed by other writers. 



The pharynx of the ticks presents no special features in its general 

 .structure. It is an elongate sack (fig. 28 A, Phy) surrounded by a 

 thick layer of constrictor muscle fibers, within which the walls, when 

 contracted, are thrown into three radial folds (L. Phy). Dilator 

 muscles arise dorsally {did) on the thickened lateral margins of the 

 subcheliceral epistomal plate (Ef>st), and ventrolatcrally (cf/i-) on the 

 lower walls of the capitulum. In Dcrmaccntor variabilis two winglikc 

 plates diverge laterally and posteriorly from the anterior end of the 

 pharynx at the base of the labrum (fig. 28 D). The similar plates 

 of D. andersoni are shown by Douglas (1943) to give attachment on 

 their concave dorsal surfaces to flat muscles (H) inserted medially 

 in the base of the labrum C'^^^^ct"). The under surface of the labrum 

 is produced into a toothlike process that fits into a groove of the lower 

 wall of the entrance to the pharynx. This structure Douglas regards 



