y8 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 1 10 



C) . The filamentous axial "stylet," in fact, is the midrib of a long, thin 

 blade that covers at least the proximal two-thirds of the hypostomal 

 gutter, the edges of which become torn by removal from the hypo- 

 stome. Whether the marginal membranes are attached to the hypo- 

 stome, or are merely closely adherent to it, the writer has not been 

 able to determine by dissection ; but Robinson and Davidson in their 

 figure of a transverse section of the capitulum of Argas persicus (fig. 

 28 K) show the "stylet" (Lm) with wide lateral expansions lying 

 free above the hypostomal gutter (hg), and the organ of Ornithodoros 

 is very clearly depicted by Bertram as a flat tapering blade (F) lying 

 over the proximal part of the gutter of the hypostome. 



Considering the relations of the "styletlike process" of the ticks to 

 the epistome behind it and to the mouth below it, there can be no 

 question that the organ so called is the labrum (fig. 27, Lm) ; it corre- 

 sponds exactly with the labrum of other arachnids, and in form is 

 suggestive of the labrum of a phalangiid (fig. 16 D, H, Lm). Borner 

 (1902) notes that the labrum of the Ixodidae is much reduced. The 

 ixodid labrum, however, though small in size, is differentiated into 

 a conical basal lobe, and a thin bladelike distal extension. The basal 

 lobe overhangs the mouth ; the apical blade, which varies in length in 

 different species, lies over the gutter of the hypostome. The covered 

 part of the hypostomal gutter is thus converted into a closed canal 

 that leads back to the mouth, and this canal, as Bertram has shown, 

 must be the food conduit (fig. 27, /^). Bertram (1939) gives a long 

 discussion of the "tongue-like process" in Ornithodoros, in which he 

 discards the impossible suggestion of Sen that the process corresponds 

 with the hypopharynx of insects ; it is difficult to see how he missed 

 the obvious fact that the organ is the labrum. 



A comparison of the mouth parts of the Ixodides with those of 

 Gamasides in which the tapering labrum reaches to the end of the 

 hypostome (fig. 24 C) will show the identity of structure in the two 

 groups. The relation of the parts in the proboscis of Laelaps 

 echidniniis is clearly seen in the figure by Stanley (fig. 28 I), who says 

 that a groove on the ventral surface of the "lingula" (labrum) ex- 

 tends into the mouth of the pharynx and probably aids in the flow of 

 blood from the wound. 



In longitudinal sections of the capitulum of Ixodides the labrum, 

 of course, looks like a stylet, and in dissections the marginal mem- 

 branes of the apical blade are sometimes lost entirely, so that the 

 axial filament appears to be a slender rod projecting from the apex 

 of the basal lobe, as it is usually shown in illustrations (fig. 28 E). 

 Moreover, the end of the organ is often broken, and may be split. 



