THE NERVOUS SYSTEM. 83 



the whole are connected by meshes of fibres, which appear 

 like strings of clear gelatinous looking nerve substance, 

 flattened and spread out in places, apparently without any 

 neurilerama (Plate VII., fig. 10). These nerves are especially 

 abundant around the ovaries and testes. 



In the larva, all the nerve centres are concentrated in the 

 anterior segments. They consist of a pair of hemispherical 

 ganglia above the oesophagus, supra-cesophageal ; and a large 

 flattened nerve centre, composed of a series, probably of 

 twelve pairs of ganglia, beneath the oesophagus, sub-cesophageal 

 (Plate VI., fig. 1). 



The supra-oasophageal ganglia are connected by a pair of 

 thick crura with the sub-oesophageal nerve centre. These crura 

 become considerably lengthened at the commencement of the 

 pupa state, and ultimately unite posteriorly, and form the 

 great cephalo-thoracic trunk, uniting the cephalic and thoracic 

 ganglia. 



The supra-cesophageal ganglia of the larva seem to cor- 

 respond to the lateral or optic ganglia of the imago. They give 

 off a pair of nerves to the rudimentary sensory organs of the 

 maggot; but I have been able to detect no commissure between 

 these ganglia, above the oesophagus. About the third day of 

 the pupa state a pair of small oval ganglia appear, uniting 

 the supra-cesophageal ganglia ; these are the rudimentary an- 

 tennal or central ganglia of the imago. They seem to bo 

 developed in the crura of the supra-cesophageal ganglia, and 

 they may exist in an extremely rudimentary condition in the 

 larva, although I have entirely failed to detect them. The sub- 

 cesophageal nerve centre consists of a series of ganglia, closely 

 united to each other, which give off twelve pair of nerves to 

 the twelve posterior segments of the larva. In the pupa it IH 



o 2 



