48'4 • ME. A. D. MICHAEL ON THE 



Along eiich lateral side of tlae triangle runs a border of clear, hyaline, flexible 

 membrane, whicli falls slightly downward, so that the whole organ forms an inverted 

 trough. 



From the lowest level of the anterior edge of the propharyngeal plate springs a half 

 moon-shaped membrane (figs. ] , 2, km), which must be regarded as forming part of the 

 epipharynx, although it is lower in level than the triangle ; it is thin, transparent, and 

 highly tiexible ; its upper surface is armed with a large number of spines ; the flexibility 

 causes this organ to hang downward, and thus the upper surface becomes the anterior 

 surface, and the spines at its edge, which are about eleven in number, come in front of 

 the opening of the pharynx, and ai^jmrently serve to stop all solid particles from 

 entering ; such particles may often be seen collected in numbers on the spines. 



The Lingua (figs. 2, 4, li) is develojoed in a very special manner in Bdella ; it springs 

 from near the lower edge of the pharyngeal opening, just as the epipharynx springs 

 from its upper edge. Where it starts from the opening it is a flat tongue with the edges 

 only slightly curled upward ; this curling upward very shortly increases, so that the two 

 edges meet and fuse, thus forming a membranous tube, which is the nature of the lingua 

 for the greater part of its length ; it is extensile, and can be extruded a considerable 

 distance beyond the mouth-oiiening (fig. i), or it can be wholly withdraw^n into the 

 mouth by invagination, being drawn inward like the finger of a glove. It is slightly 

 enlarged at the distal end, and is capable of motion and flexion in every direction ; it is 

 composed of thick membrane and provided with delicate muscles. 



From each side of the lingua, near where it springs from the oesophagus, a fine 

 tendinous " tie " (fig. 2, tt) runs upw'ard to tlie base of the epipharynx, and nearly between 

 these two ties a transverse line of minute tooth-like, but not pointed, projections runs 

 across the base of the lingua ; probably the teeth at the edge of the semilunar membrane 

 of the epipharynx meet these projections. 



This lingua is tJie organ through which the juices of the victims are sucked, the 

 pharynx being the pumping-organ ; in specimens killed w bile feeding, or shortly after, 

 the tubular lingua is often found full of the same food-material as that in the pharynx, 

 sucking-stomach, and oesophagus. 



Kramer (ii) saw and has figured the lingua extended (his fig. 5, e); he figures and 

 describes two appendages above its base Avhich he calls " wing-shaped," and supposes to 

 be cuticular, but which I have not ever seen. Karpelles also has figiu-ed the lingua 

 ihis fio'S. 2, 4, 7, 8, ce), but he calls it tiie " oesophagus " ; it cannot be considered as part 

 of the oesophagus, because it is anterior to the pharynx and is situated in the mouth- 

 cavity, lying, w^hen retracted, within the trough of the maxillary lip. 



The Alimentary Canal and Excretory Organ. 

 (Figs. 1, 2, 3, 4, 5, 6, 7, 34, 41, 42, 43.) 



In the whole of the " Trombidnim " group of Acarina, and also in the Gamasidae and 

 some other families, it is impossible to treat these as separate sets of organs, they are so 

 closelv connected as to form one and must be dealt with together. 



