7 8 THE LARVA OF THE BLOW- FLY. 



reference to Fig. 14, 2, which represents a transverse section 

 through the region indicated by the line 2 in Fig. 13 : cp is the 

 cephalo-pharyngeal band ; sp, the suspensory membrane, and a, 

 the base of the antennal rudiment. 



There is a large blood sinus between them, in which the 

 oesophagus lies, into which the dorsal vessel opens through the 

 ring. The suspensory membrane, sp, forms its roof, and the 



rt. 



FIG. 1 3.- -A semi-diagrammatic representation of the Head Discs and Hemispheres 

 seen from above : / 2 and j, planes of the sections i 2 and j in Fig. 14 ; 

 mx, maxillary disc ; ph. pharyngeal ; a, antennal ; o, optic discs ; pf, prefacial 

 rudiment ; cp, cephalo-pharyngeal braid ; cr, crop ; c //, cerebral hemisphere ; rt, 

 retina ; o s, optic stalk ; p s, provisional sac. 



discs its lateral walls. The inner and posterior part of the wall 

 of the disc sac is occupied by the epiblast of the disc ; its outer 

 wall is the provisional membrane. 



The Ring was first described by Weismann as follows [2, 

 p. 125]: 'The anterior part of the dorsal vessel lies above the 



