SENSE OEGANS. 175 



2. The ventral chain. 



Fix the cockroach luith the dorsal surface uppermost : re- 

 move the gizzard, mescnteron, and proctodaum ; 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 lie 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. 

 8. 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 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 back- 

 wards on the oesophagus, beneath the supra-oesopha- 

 geal ganglia, from which it receives a pair of gan- 

 gliated nerve trunks ; it then continues its course 

 backwards, as a median nerve, along the (Esophagus 

 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 back- 

 wards 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 fenestree are perhaps sense organs, but their func- 



tion is unknown. 



