THE HEAD AND MOUTH ARMATURE. 



45 



The Labral Sclerite of the newly-hatched larva (Figs. 7, in, and 9, 2, in) 

 articulates by a pair of processes with the anterior inferior processes of the 

 cephalo-pharynx ; these form the edges of the true mouth. 



The Great Hooks (Fig. 9,3-, h) present three processes : a head which 

 articulates with the hypostomal sclerite, a coronoid process above, which 

 gives insertion to the retractor muscle, and a discal process below, which is 

 adherent to the centre of the stomal disc. 



In the adult larva a pair of small sclerites are found lying side by side in 

 front of the crossbar of the hypostomal sclerite ; they are the points of inser- 

 tion for the retractor muscles of the labium. 



Fig. 9. — I, the cephalo-pharynx and mouth armature of a newly-hatched larva ; 

 2, the mouth armature of the same, seen from its ventral surface ; 3, the same 

 parts from the adult larva seen in profile ; 4, a diagrammatic section through the 

 thickest part of the cephalo-pharynx ; 5, the head capsule of Pcecilostola, after 

 Brauer ; 6, the internal head skeleton of the Cossus larva, after I>yonet — w, 

 median ; h, lateral hooks ; //, pseudo-tracheae ; fl, pseudo-labrum and discal 

 sclerites ; x, parastomal y, hypostomal, sclerites ; cl, clypeus ; z' and 2", Zopf- 

 griiten or cephalo-phaiyngeal processes ; f, lateral plate ; iph, pharyngeal sinus 

 and muscles of the epipharynx. 



The pharynx (Figs. 8 and 9, ^) lies between the inferior processes of 

 the cephalo-pharynx. In transverse section its cavity appears nearly cre- 

 scentic. The concavity of the crescent is filled by the pharyngeal sinus ; its 

 lower wall is formed by a plate developed in the cuticle of the alimentary 

 tube, the hypopharynx. The upper surface of the hypopharynx exhibits a 

 series of longitudinal T-shaped ridges, which project into the oesophageal tube. 



