SENSE ORGANS. 183 



2. The ventral chain. 



Fix the cockroach with the dorsal surface uppermost ; 

 remove the gizzard, mesenteron, and proctodeum ; and turn 

 the crop aside. 



The ventral chain consists of a double series of 

 ganglia, with double connectives, running along the 

 ventral wall of the body. 



A pair of closely apposed ganglia he in each of 

 the three thoracic segments, and a pair of smaller 

 ganglia in each of the first six abdominal segments. 

 The last pair are the largest of the abdominal ganglia, 

 and give off nerves to the various parts of the sixth 

 and succeeding segments. 



3. The visceral nervous system arises as a pair of nerves, 



one from the anterior part of each para-cesophageal 

 connective. The two nerves, after giving off a pair 

 of the nerves to the labrum, unite in the frontal 

 ganglion, a small median ganglion on the anterior 

 wall of the oesophagus, just below the antennary 

 lobes. From this ganglion a median recurrent nerve 

 runs backwards on the oesophagus, beneath the 

 supra-cesophageal ganglia, from which it receives a 

 pair of ganglionated nerve-trunks ; it then continues 

 its course backwards, as a median nerve, along the 

 oesophagus and crop to a small triangular ganglion 

 on the dorsal surface of the crop, about the middle 

 of its length. From this ganglion two branches run 

 obliquely backwards over the surface of the crop. 



E. Sense Organs. 



1. The tactile organs have already been examined. They 



are the antennae, the maxillary palps, the labial 

 palps, and the anal cerci. 



2. The eyes are very large compound organs which agree 



in essential characters with those of the crayfish. 

 The corneal facets are hexagonal. 



3. The fenestra are perhaps sense organs, but their func- 



tion is unknown. 



