168 THE EMBRYOLOGY OF THE HONEY BEE 



TraTr 



ATraL 



Ten.. 



PTraL 



Fig. 63. Side view of larva about two and one-half days old, treated 

 with caustic potash, showing tracheal system. 



branches are also sent off by the ventral commissures. At the 

 anterior end of each of the lateral trunks a large branch arises 

 which passes cephalad and breaks up into two smaller branches, 

 both of which run cephalad, one in contact with the inner sur- 

 face of the optic lobe, the other parallel to the mandibular apo- 

 deme and close to it. Mesiad of this large branch is a smaller 

 branch which is sent off by the anterior tracheal commissure. 

 This also extends cephalad supplying the dorsal part of the head. 

 A third branch arises from the ventral side of each of the lateral 

 trunks just cephalad of the first pair of stigmata and dividing, 

 supplies both the base of the labrum and the ventral portion of 

 the first trunk (thoracic) segment (Fig. 64). 



The tracheae are simple in structure, being merely tubes com- 

 posed of a single layer of epithelial cells continuous with those 

 of the hypodermis at the spiracles and lined by chitin thickened 

 in the form of fine transverse threads, more or less spirally ar- 

 ranged, the taenidia (Fig. 65, Tac). 



