32 THE INTERNAL STRUCTURE OF MUSCA DOMESTICA 



plasniic fibres anastomose with each other. Among these smaller 

 cortical cells, and also occasionally in the ganglionic substance, 

 large ganglionic cells occur, their protoplasm taking the stain 

 very readily. Unipolar, bipolar, and tripolar ganglion cells are 

 found. 



The Eyes. Each eye contains about 4000 facets. They are 

 similar in all respects to the eyes of the blow-fly, which have 

 been fully described by Hickson {loc. cit), whose results my study 

 confirms ; consequently a description of their structure will not 

 be given. It should be noted that, in spite of the fact that 

 Hickson corrected many mistaken views held by Lowne in his 

 memoir (1884), these are repeated in his later monograph of 

 the blow-flv. 



The cephalo-thoracic nerve cord (fig. 8, c.n.) unites the 

 cephalic and thoracic ganglia. Near its juncti(jn with the 

 thoracic ganglion a pair of cervical nerves (cer.n.) arise, inner- 

 vating the muscles of the neck. 



PrC. ms.d 



, ab.n 



i Ms.G. 1 Mt.G. rnlcr 



Fig. 9. Thoracic compound ganglia. Left aspect. 

 Lettering as in figs. 8 and 10. 



The Thoracic ganglion (figs. 8, 9, 10) is pyriforra, with the 

 broad end anterior, and rests on the entothoracic skeleton of 

 the mesothorax. As in the cephalic ganglion, the component 

 ganglia are ensheathed in a cortical layer, which is of the same 

 nature as that of the cephalic ganglion. The nerves of the 

 three pairs of legs (pr.cr., ms.cr., mt.cr.) arise from three large 

 ganglia, which are the prothoracic (Pr.G.), mesothoracic {Ms.G) 

 and metathoracic (Mt.G.) ganglia. These are united by a median 

 longitudinal band of nerve tissue, which runs dorsal to them, and 

 behind the metathoracic ganglia swells out into a ganglionic mass 

 (A.G.) which represents the abdominal ganglia. In this median 

 dorsal band thcic is a median dorsal fissure stretching posteriorly 



