ANATOMY. 



21 



organs of the two sides are connected in two places only. The halves 

 of the mentum have a cross-connection below, near the middle, and 

 both vertical plates are attached to a single ''latticed process." There 



Mouth hook 



Fig. 2. — Cephalopharyngeal skeleton of third-stage larva of Drosophila 



melanogaster. 



Fig. 3. — Cephalopharyngeal skeleton of third-stage larva of 



Drosophila funebris. 



Fig. 4. — Cephalopharyngeal skeleton of third-stage larva of 

 Scaptomyza adusta. 



is also an unpaired prementum, not shown in these figures, lying be- 

 tween the halves of the mentum and at the level of the apex of the 

 lateral process. 



Fabre believed that the corresponding apparatus in the blow-fly 

 served as an organ for locomotion rather than for mastication. Ob- 

 servation of living Drosophila larvae has convinced me that, in this 

 group at least, mastication is its primary function. Locomotion is 

 usually accomplished by the help of the backward-pointing ventral 



