NERVOUS SYSTEM 29 



3. The segmental muscles. These muscles, which are sa 

 prominent in the larva, have almost disappeared in the imago. 

 They are represented by the cervical muscles, certain small 

 thoracic muscles, the thoraco-abdominal muscles, and the seg- 

 mentally-arranged abdominal nuiscles, together with the muscles 

 controlling the ovipositor and male gonapophyses. 



4. The muscles controlling the thoracic appendages, the 

 wings, legs and halteres. There is an elaborate series of muscles 

 controlling the roots of the wing, but in order to avoid too much 

 detail they will not be described here. The flexor muscles of 

 the anterior coxae have their origin on the inner surfaces of 

 the humeri, a fact supporting the prothoracie nature of these 

 sclerites; the flexors of the middle pair of legs have their origin 

 on the sides of the posterior region of the prescutum. The 

 internal muscles of the leg are similar to those of the blow-fly 

 and Volucella. 



5. Special muscles. These are the muscles controlling the 

 spiracular valves, the penis, and other small muscles. 



The Nervous System. 



The central nervous system (fig. 8) consists of: (1) the brain 

 or supraoesophageal ganglia, which are closely united with the 

 suboesophageal ganglia, the whole forming a compact mass which 

 I propose to call the cephalic ganglion (fig. 8, C.G.), perforated 

 by a small foramen for the passage of the narrow oesophagus, and 

 (2) the thoracic compound ganglion, which is composed of the 

 fused thoracic ganglia with the abdominal ganglia. The two 

 compound nerve .centres are united by a single median ventral 

 cord running from the suboesophageal ganglia to the anterior 

 end of the thoracic nerve-centre. 



The cephalic ganglion consists of the supraoesophageal ganglia 

 and the suboesophageal ganglia so closely united that the commis- 

 sural character of the circumoesophageal connectives is completely 

 lost. Externally on the dorsal side of the brain three longitudinal 

 fissures can be seen, a median fissure and two lateral fissures 

 marking the origin of the optic lobes. 



