(22) 



416 C. GORDON HEWITT. 



two pairs have their upper ends attached to the prescutum 

 and scutum, and their lower ends inserted on the mesosternum, 

 the third pair is attached dorsally to the scutum and ventrally 

 to the lateral plate of the postscutellum above the spiracle. 

 As Hammond has shown in the blowfly (1881) all these 

 muscles are mesothoracic. The dorsales by contraction 

 loosen the alar membrane and so depress the wing, the 

 sternodorsales have the opposite effect. 



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

 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 

 segmentally-arranged abdominal muscles 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 coxa3 have their origin on the 

 inner surfaces of the humeri, a fact supporting the pro- 

 thoracic 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 blowfly and Volucella. 



5. Special muscles. These are the muscles controlling the 

 spiracular valves, the penis, and other small muscles. 



2. The Nervous System. 



The central nervous system (fig. 11) consists of (1) the 

 brain or snpracesophageal ganglia which are closely united 

 with the suboesophageal gnnglia, the whole forming a compact 

 mass which I propose to call the cephalic ganglion (fig. 1, 

 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 



