EXTERNAL ANATOMY OF INSECTS. 363 



of Aphaniptera (Pulex L.), in which the ordinary 

 Tropin are replaced by a bivalve beak, between the 

 valves of which there appear to be three lancets a . 

 It includes the Lamina, Scalpella, and Ligula. 



A Lamina (the Lamina). Two corneous plates which 

 are laterally affixed to the mouth of a flea, proba- 

 bly representing the Mandibula of the perfect 

 mouth, which somewhat resemble the beak of a 

 bird b . 



B Scalpella (the Lancets). The two upper or outer 

 instruments, probably for making an incision in the 

 skin ; these are flat and acute, and seem to repre- 

 sent the Maxilla of the perfect mouth c . 



C Ligula (the Ligula). A capillary instrument between 

 the lancets; probably representing the tongue of 

 the perfect mouth d . 



6. Rostellum (the Rostellum). The oral instruments 

 of Pediculus and some other Aptera, in which the 

 ordinary Tropin are replaced by an exarticulate re- 

 tractile tube, which exerts a retractile siphuncle. 

 It includes the Tubulus and Siphujiculus. 



A Tubulus (the Tubulet). The tube or retractile base 

 of the Rostellum. 



B Siphunculus (the Siphuncle). The real instrument 

 of suction, which when unemployed is retracted 

 within the tubulet. 



Besides the above variations from the type of what I 

 call a Perfect Mouth, there are others in which the parts 

 of the Trunk appear to aid in the conversion of the food, 



a Plate VII. Fig. 8. *> Unci. c'. 



c Ibid. cl'. Maxillary Palpi h". d Ibid. e'. 



