42 THE LARVA OF THE BLOW-FLY. 



In front of and above this median tooth there is a remarkable 

 invagination of the hypoderm (Fig. 7, in) which extends over 

 the pharynx, and communicates with the sac from which the 

 imaginal discs of the head of the nymph are subsequently deve- 

 loped. This invagination is undoubtedly the fore-head (Vorder- 

 kopf) of the embryo, which is invaginated between the maxilla;. 



Below the median tooth is the true mouth orifice. The tooth 

 itself is clearly the labrum, or upper lip ; with which, I think it 

 extremely probable, the mandibles are fused, although the 

 evidence of this is obscure. 



Fig. 8. — Sections of ihe bead of the adult larva (40 diam.) — i, a vertical median 

 section ; sd, stomal disc ; 2, a transverse section in the line -v x' in I. The 

 curve is due to the position of the heal, that represented in Fig. 4, C ; h, the 

 great hook ; hy, hypostomal sclerite ; m, mouth ; //;, pharynx ; cp, anterior 

 inferior process of the cephalo-pharynx ; rt', oesophagus ; sd, salivary duct. The 

 section shows the grooves in the hypopharynx — 3, section through the mouth and 

 pharynx, in the line j'^' in I, showing imaginal discs I. 



Below and behind the labrum is the orifice of the salivary 

 duct in the rudimentary ligula, which is undoubtedly the homo- 

 logue of the ligula of the caterpillar, Figs. 6, 7 and 8. 



In the newly-hatched larva the stomal discs are relatively 



