532 MEDICAL ENTOMOLOGY 



parts, which is quite unlike that in those arthropods previously considered, 

 is" best studied in sections of the head. 



In a transverse section of the head anterior to the point of insertion 

 of the antennae (Plate LXVII, fig. 2) two separate canals are seen in 

 the middle line, J:he upper one of which occupies 

 Tranwertt sections a pp rox i ma t e iy the middle of the section, and is larger 

 and has thicker walls than the other. The upper canal, 

 when traced backwards, is found to become continuous with the oesopha- 

 gus, which lies, in the posterior part of the head, in its normal position 

 dorsal to the brain, and eventually dips between the supra- and infra- 

 oesophageal ganglia to reach the neck. This canal is evidently a part of 

 the stomodaeum, and from the numerous muscles which are attached to 

 it, as will be seen presently, one can assume that it forms a sucking 

 apparatus of the usual pattern, and that it can be moved in a forward 

 direction. Within the cavity of the lower tube there are several minute 

 chitinous structures cut in section ; these are the mouth parts, probably 

 corresponding to the first maxillae, the labium, and the hypopharynx 

 of other insects. The wall of the canal in which they lie can be traced 

 to the anterior end of the head, where it opens at the' same point as the 

 upper canal ; posteriorly it terminates at the level of the brain, by fusing 

 with the thickened posterior ends of the mouth parts themselves. The 

 mouth parts are thus enclosed in a ' proboscis sheath ', which is in 

 reality nothing more than an invagination of the integument around 

 them. 



The apparatus for the ingestion of food therefore consists of two parts, 

 which may be considered separately. The sucking apparatus is easily 

 dissected out of the head in cleared preparations, as 

 apparatus * ts wa ^ * s cn it mous throughout. When isolated and 

 straightened out (Plate LXXI, fig. 3) it is seen to 

 consist of two distinct chambers, which are connected with one another by 

 a membraneous canal. Anticipating the description of the musculature 

 of these chambers, they may be called the buccal cavity and pharynx 

 respectively, using the terms in the sense in which they have been used 

 in the account of the sucking apparatus of the Diptera. The buccal 

 cavity, or first chamber, is elongate, four or five times as long as broad, 

 and is strongly chitinized. The borders are thickened into conspicuous 

 ridges, and at the -posterior end these are produced in a backward and 

 "outward direction as pointed cornua. The membraneous canal which 

 connects the two chambers is about half the length of the buccal cavity 

 when its natural bend is undone. The pharynx is pear-shaped, and 



