EXTERNAL ANATOMY OV INSECTS. 465 



the term, therefore, may be applied to represent a diffe- 

 rent set of tropin, without any risk of producing confu- 

 sion. This part consists of Jive pieces : viz. a minute, 

 long, conical piece, commonly very slender, which covers 

 the base of the promuscis, and represents the labrum a ; a 

 jointed sheath (vagina), consisting of either three or four 

 joints, the analogue of the labium, and four slender rigid 

 lancets (scalpella), the two exterior ones, according to 

 M. Savigny, representing the mandibles, and the inter- 

 mediate pair the maxilla; b . By the union of these four 

 pieces a suctorious tube is formed, which the animal in- 

 serts into the substance, whether animal or vegetable, 

 the juices of which form its nutriment. These pieces are 

 dilated at their base, and serrated at their apex ; and the 

 two central ones, though at their origin they are asun- 

 der, form one tube, which has often been mistaken for a 

 single piece. A pharynx and tongue have been disco- 

 vered by M. Savigny in this apparatus ; who thinks that 

 in Nepa there are also rudiments, but very indistinct, of 

 labial palpi : so that the maxillary j^olpi seem to be the 

 only part absolutely wanting c « 



The Promuscis when at rest is usually laid between 

 the legs; but when employed, in most cases its direction 

 is outward. In the genus Chermes L. [Psylla Latr.) the 

 origin of the promuscis has been supposed to be in the 

 breast; but if closely examined, this anomaly in nature 

 will be found not to exist. If you take one of these in- 

 sects, the first thing that strikes you upon inspecting the 

 head, is a pair of remarkable conical processes into which 



a Plate VI. Fig. 7. a'. 



b Ibid. Labium b'. Mandibular c'. Maxilla? d'. 



c Savigny Anim. sans Vertebr. I. i. 37- 



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