INTERNAL ANAT03IY OF BDELLA. 483 



Palpi. — To the hind corners of the maxillary lip the well-known " antenniform palpi " 

 of JBclella (fig. 4, P) are jointed, not directly to the hard cliitin of the lip, but by means 

 of the intervention of some flexible cuticle, which doubtless gives greater freedom of 

 motion to these highly mobile organs. The palpi of Bdella differ from the corre- 

 sponding parts in other Acarina, both in their great length and size, and in the position 

 in which they are carried. The length is almost equal to that of the front legs in most 

 species ; and the pi'oportionate length of the joints and the arrangement of the hairs or 

 spines upon them form good and much-utilized specific distinctions. The three proximal 

 joints are usually carried pointing almost perpendicularly upward, while the two 

 terminal joints point almost horizontally forward or a little downward. 



The Mandibles (figs. 30 md and 31) lie close together upon the roof of the rostrum ; they 

 differ from those of all other Acari, except the Ixodidte and a few isolated species such 

 as Nicoletiella, (Zabidophorus, Kramer), in not being enclosed within the chitinous case 

 of the rostrum, but being quite free and resting on the toji of it ; they are two-jointed 

 chelate organs, the movable joint being placed ventrally, as is usual amongst Acarina. 

 The chelae are extremely small and fine in most species ; and, in such as I have dealt 

 with, simple without teeth. The mandibles are not eaj)able of being retracted into the 

 body, as are those of the Gamasidfe and others ; indeed, the bulbous form of their proximal 

 ends would prevent this ; but the whole rostrum can to some slight extent be with- 

 drawn into the camerostrum. The inner and lower sides of the mandibles are 

 almost flat ; the outer and upper sides curved — in fact one continuous curve forms 

 the two. The shape of the mandibles and distribution of the hairs ujdou them are relied 

 on for specific distinctions, and indeed the form is considered a generic distinction by 

 some a^^thors. 



Between the two mandibles is a thin low jmrtition (fig. 30, ^;m) like a blade on edge ; 

 this is the " tastcrformiges Organ " of Karpelles : I do not, however, see any evidence 

 of its being of a palpus-like or tactile nature ; I am rather inclined to regard it as a 

 simple partition which separates and guides the mandibles, and prevents their rubbing 

 against each other ; it is not attached to the mandibles. 



The Epipharynx is an organ of considerable importance and complexity, which appears 

 to have been entirely overlooked by Kramer, Berlese, and Karpelles. It springs from 

 the anterior edge of the propharyngeal plate (figs. 1, 2, p)p), oi") rather, by means of a 

 fold from the membranous sac which encloses the pharyngeal muscles a trifle above the 

 propharyngeal plate ; thiis it projects into the mouth-cavity and overhangs the opening 

 of the pharynx. It consists in B. Basferi of a very elongated, almost triangular piece 

 which ends anteriorly in an extremely fine point; it is about "25 mm. long, and 

 abou.t "07 mm. wide at the base. This central triangle is stiff and lancet-like; it is 

 thickest in the median line, where there is a slight tendency to a longitudinal ridge in 

 the posterior part of the organ ; to this ridge it slopes uji gently from the sides, but the 

 median thickening is not great or conspicuous. The whole of the triangle, except its 

 anterior end, is semiopaque, and is thickly and irregularly dotted with red pigment ; 

 the pointed anterior end is of clear hard chitin. The ducts (fig. 2, dp) from the pedcibal 

 salivary gland discharge on the underside of this triangle close to the hind angles 



