THE NEBVOU8 8YBTEM. 79 



indicates the division of the two ganglia ; the nerve to the 

 ocelli appears to arise from this groove, but has more pro- 

 bably a deep origin from the optic ganglion. Anteriorly, the 

 central ganglia are hollowed out for the reception of the 

 anterior ganglia ; beneath this hollow they give off the great 

 antennal nerves. I have observed slight convolutions situated 

 in the interior of the central ganglia, on making a section 

 through them. 



The anterior or cerebroid ganglia (Plate VII., figs. 2 and 4) 

 are very remarkable nerve centres, supported on a pair of 

 round peduncles, deeply convoluted and united by a well 

 marked commissure in the mesial line. These give off no nerves, 

 and their peduncles seem to arise partly in the substance of the 

 central ganglia, and partly from the thoracic nerve trunk. 

 They are best seen by making vertical sections of the whole 

 cephalic nerve centre after hardening in spirit; but may be 

 seen very frequently by carefully compressing the hardened 

 nerve centre between the slide and thin glass. Their demon- 

 stration is not very easy without great practice, owing to their 

 being imbedded in the central ganglia. 



The lateral ganglia form an ovate mass on either side of the 

 central ganglia. They differ in no way apparently, as far as 

 structure is concerned, from the other ganglia ; but they are 

 covered externally by a thick layer of nerve cells, very largely 

 supplied with trachea 1 vessels, which form long loops parallel 

 to each other. They give origin externally to the nerves of the 

 compound eyes. 



The cephalic nerve centre is supplied by very minute tracheal 

 vessels. These arise from the great tracheal sacs, which almost 

 entirely invest it. 



The oosophageal nerves appear close to the under side of the 



