140 THE INTEGUMENTAL SKELETON OF THE IMAGO. 



The separation of the sclerites forming the upper and lower 

 surface of the labrum gave rise to the view that one pair repre- 

 sent the labrum and the other the epipharynx. As the labrum 

 does not consist of a single plate in any insect, but is always a 

 hollow process, this is not a tenable view (Kraepelin [70]). 



The external (dorsal) pair of sclerites are fused together at 

 their proximal extremity, where they articulate with a pair of 



Fig. 29.—/, A section throiigh the mouth in the plane a little below that marked by 

 the line pi, Plate VI. ; w, cavity of the prelabrum containing muscles ; «, edges 

 of the groove in the theca ; </, dorsal, and o, oral sclerites ; /, the ligula and 

 salivary duct ; //, the hypoglossa, and pa, the paraphysis. The cavity c is cut oil 

 from the alimentary lube when the ligula is brought into contact with the 

 labrum ; it is indicated by the letters st in Plate VI. 3, A section through the 

 anterior dorsal edge of the oral sucker, showing the dislocated bead and furrow 

 which closes the prestomum and the lower edge of the hypoglossa; the lips 

 are strongly flexed on the theca: /;, hypoglossa ; /a, paraphysis; d s, discal 

 sclerile ; pt, pseudotrachea; ; pst, prestomum. J, A section through the haus- 

 tellum near the plane sg in Plate VI. : //, prelabrum ; th s, thyroid shield ; 

 ;«i to ni\ muscles in the cavity of the theca ; e, elastic band. 'I"he ligula is 

 seen between the hypoglossa and the prelabrum. 



apodemes— the glosso-pharyngeal apophyses of Straus Durck- 

 heim already referred to (Fig. 27, ap). These lie in the cavity of 

 the rostrum, and are the ' nail-like pieces ' which Gerstfeldt 

 thought analogous to the cardines of the maxilla;. 



As the cardines of the maxillae represent the hollow basal 

 joint of a ventral appendage, no possible modification of them 

 could produce a mere internal apodeme ; and, further, the 

 cutaneous attachment of these apodemes in front of the palpi- 

 gerous scale entirely precludes such a view of their nature. 

 Menzbier, I think correctly, regards them as simple muscle 

 tendons [50, p. 65]. 



