176 



[CH. 



76, 77, Vr), a short white loop which appears to be the severed 

 anterior end of the visceral trunk. If that be so, the connection of 

 the visceral trunk with the pedal tracheae is a secondary formation. 

 Tracheation of the Head (fig. 77). The labium is supplied by 

 a pair of strong tracheae, which arise from a transverse loop, 

 derived from the two first pedal tracheae close to their bases. 

 All the rest of the head is supplied by the two pairs of large dorsal 



Fig. 77. Tracheal system of head and part of thorax of larva of Synlestes weyersi 

 Selys ( x 13). ant antennary trachea; ao anterior optic trachea; c cerebral 

 trachea; E eye; / frontal branches; Ib labial tracheae; loc lateral ocellus; 

 moc median ocellus; og trachea to optic ganglion; p lt p 2 pedal tracheae; 

 pi branches to postocular lobe; po posterior optic trachea; SA superior 

 anastomosis ; S^ mesostigma ; TA thoracic anastomosis ; Vr visceral remnant. 

 Original, cedar oil preparation. 



trunks. Of these, the two uppermost, soon after entering the head, 

 are united by a semicircular arch, the superior anastomosis (SA). 

 From the two bases of this arch, large tracheae pass transversely 

 outwards to supply the eyes, giving off branches to the postocular 

 lobes by the way. Higher up on each side of the arch, smaller 

 branches pass outwards and forwards to the anterior region of the 

 eye. At the summit of the arch, in Zygoptera, two small tracheae 



