TRACHEAL SACS OF HEAD 45 



fill up all the space which would otherwise l)c haemococl. These 

 tracheal sacs are supplied by the tracheal ducts which, on entering 

 the head capsule, curve dorsally behind the cephalic ganglion. 

 Before curving upwards each gives off a large ventral duct (fig. 19, 

 tn.d.) which spreads out beneath the cephalic ganglion, forming a 

 structure of a tentorial nature upon 

 which the ganglion rests. The dorsal 

 cephalic ducts unite behind the ce- 

 phalic ganglion above the oesophagus. 

 From the point of junction three 

 ducts arise, two lateral ducts and a 

 median dorsal duct. The median 



dorsal duct (m.d.) opens into a large tj,^ m t> ^ ■ *• *i 



^ . o riG. 19. Posterior view ot the 



bilobed dorso-cephalic sac lying on tracheal duets which supply the 



r. . , , • 1 . cephalic sacs and tracheae. 



top of the ganglion, and occupying ,..(,.. Cervical tracheae which fuse 



the dorsal region of the head capsule. ^^^^'^ the oesophagus on the pos- 



. II- terior side of the cephalic gang- 



It gives off branching tracheal twigs lion. l.d. Lateral duct. 



supplying the antero-doi-sal portion 'll^^^l^ tt which 



of the optic ganglion (periopticon). spread out beneath the cephalic 



Each of the lateral ducts (l.d.) sup- ^^"^ ^°^^' 

 plies the posterior cephalic sacs. It first communicates with a 

 sac (fig. 17, p.c.s.) lying behind the dorsal portion of the optic 

 ganglion to which it gives off a large number of tracheal twigs. 

 This sac opens into an elongate vertical sac which occupies the 

 ventro-posterior region of the head capsule. The remaining 

 tracheal sacs of the head are supplied by the tentorial tracheal ducts 

 (fig. Id, tn.d.), which spread out beneath the cerebrum in a fan-shaped 

 manner and are bilaterally distributed. Each half, in addition to 

 giving off internally tracheal twigs to the optic ganglia, communi- 

 cates with two tracheal sacs. An internal duct leads into a large 

 spherical sac, the anterior cephalic sac (fig. 17, a.c.s.), situated in the 

 anterior region of the head dorsal to the fulcrum. From the dorsal 

 side of this sac a branch is given off which supplies the antenna of 

 its side; the ventral side is continued down the fulcrum as a narrow 

 tracheal sac. The lateral portion of the tentorial tracheal duct opens 

 into the ventro-lateral cephalic sac (v.s.c.) situated posterior to the 

 optic ganglion. The lower end of this sac gradually narrows as it 

 enters the rostrum which it traverses, giving off half-way along 



