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 through the mouth in the plane a little below that marked by 

 the line pi, Plate VI. : m, cavity of the prelabrum containing muscles ; a, edges 

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

 salivary duct ; h, the hypoglossa, and pa, the paraphysis. The cavity c is cut off 

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

 labrum ; it is indicated by the letters st in Plate VI. 2, 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 : /i, hypoglossa ; pa, paraphysis ; d s, discal 

 sclerite ; ft, pseudotracheae ; pst, prestomum. j, A section through the haus- 

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

 in 1 to >//'*, muscles in the cavity of the theca ; e, elastic band. The 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 maxillae. 



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] . 



