142 THE INTEGUMENTAL SKELETON OF THE IMAGO. 



plates (Fig. 28, ./, ds), discal plates the ' Obere Chitingabel ' of 

 Kraepelin, which support the pseudotracheas and the teeth. 



The Thyroid is a shield-like convex plate which covers the 

 whole of the ventral and lateral surfaces of the theca (Fig. 30, 4}- 

 It terminates distally in a pair of divergent processes, or cornua ; 

 these articulate with grooves in the furca (Fig. 28,5). Its lateral 

 margins are strengthened by two strong internal ridges which 

 terminate in the cornua (Fig. 30, /,/). The thyroid is developed 

 after the insect emerges from the pupa, only its cornua are 

 already present in the very young imago. 



FIG. 30. Details of the haustellum : /, the prelabrum and ligula : a, external, and 

 l>, internal plate, the labrum and epipharynx of Menzbier ; c, part of the pre- 

 pharyngeal tube ; d, the ligula ; 2, the prelabrum seen from in front ; j, the 

 external plate, labrum of Menzbier ; 4, part of the thyroid sclerite : e, body of 

 the sclerite ; f, lateral ridges ; g, inner, and h, outer supports of the cornu ; i, 

 the cornu ; k, the furca ; /, groove in which the cornu is lodged. 



In the well-known preparations made by the late Mr. Top- 

 ping, the thyroid shield is undeveloped, and the preparations 

 exhibit other evidences of having been made from flies almost 

 immediately after their escape from the pupa. The facial 

 sclerites and the epistome are undeveloped ; the furca has also 

 been cut through in the middle line, probably with a pair of 

 scissors with very small strongly-curved blades or by a V- 

 shaped incision made close to the junction of the theca and the 



