436 TV//; -\7f A' [ 'O US S ) V> Tl-'.M. 



equal to the former in size, which divides into a number of 

 fasciculi, some of which are lost in the cellular cortex, whilst 

 others enter the corresponding reticular enlargement of the 

 stroma. 



The nerve to the halter has only one root, which is similar 

 to the ventral root of the pro- and meso-thoracic dorsal nerves; 

 it arises from the great ganglion of the halter, partly from the 

 central stroma and partly from the cortex (see ' Physiology of 

 Nervous System '). 



The remaining nerves may be termed the anterior (ad') and 

 posterior (ad") accessory dorsal, and the first pair of abdominal 

 nerves (ab'). 



The accessor}' dorsal nerves arise from the lateral region 

 of the thoracic ganglion, between the dorsal and ventral nerve 

 roots. As only two pairs are developed, which terminate near 

 the spiracles, it is highly probable that they supply the 

 spiracular muscles, but owiner to their extreme fineness I have 

 been unable to trace them into these muscles. 



The abdominal nerves of the thoracic ganglion are two in 

 number, one on each side (ab'), they pass beneath the meso- 

 phragma, and are distributed to the muscles and skin of the 

 basal part of the abdomen. 



The dorsal band, much reduced in size, is continued as a 

 single nervous trunk, the abdominal cord, which gives off four 

 pairs of nerves in the abdomen, and terminates in several 

 branches. 



According to Meigen, quoted by Bunneister [8], the Blow- 

 fly has two small ganglia on the abdominal nerve-cord, one in 

 the second abdominal segment, and one between the ovaries 



KII' I I' >\ <>! 1'l.A I I. \.\YI. 



The central nervous system of the imago seen from its dorsal aspect. 



a, antennal nerves ; ah', abdominal nerves arising from the thoracic nerve 

 centre; ab" to ah'", abdominal nerves arising from the ventral abdominal nerve 

 cord ; ad' , a</", anterior and posterior accessory dorsal nerves ; </', </", </"', pro-, 

 meso- and meta-thoracic dorsal nerves; in -\, maxillary nerves; o, ocelli; 

 or, cesophageal opening between the crura ; g, optic ganglia ; o >i, optic nerve : 

 />/i, pharyngeal nerves; :', i/' v'" , ventral thoracic nerves. The hemispherical 

 cap-, on the optic nerves represent the ret in . 



