i62 COMPARATIVE ANATOMY 



passing forward from the mesothorax. The minute ramifica- 

 tions of the tracheae extend to every organ of the body, into the 

 nervures of the wings, and into the long filiform antennae. 



The nervous system of the cockroach (fig. 39, C) is con- 

 structed on the same plan as that of the Crustacea, consisting 

 of a supracesophageal ganglion connected by cords passing 

 round the gullet with a ventral ganglion chain, and, in addition, 

 a stomatogastric nerve plexus. The supracesophageal ganglion 

 of the cockroach lies in the head, and is large and complex, 

 consisting of three pairs of fused ganglion masses known as the 

 proto-, deuto-, and trito-cerebrum. It gives off nerves to the 

 eyes and antennae, and is connected by a pair of very stout 

 cords passing round the gullet with a large subcesophageal 

 ganglion mass, also lying in the head immediately in front of 

 the sub-mentum. The subcesophageal ganglion innervates the 

 mandibles, maxillae, and labium, and is joined by a long and 

 slender pair of connectives with the first thoracic ganglion-pair 

 lying in the prothorax. There is a large ganglion-pair in each 

 thoracic segment, and in each of the first six abdominal 

 segments, the last of the series being large, and supplying 

 nerves to its own and the posterior segments of the body. 



The stomatogastric system is highly developed. Two short 

 nerves pass from the pericesophageal connectives to a frontal 

 ganglion situate^ in the head on the dorsal side of the gullet, 

 and from this gafjglion a median recurrent nerve runs back to 

 a visceral ganglion lying on the upper side of the crop. From 

 the visceral ganglion a stout nerve runs outwards and backwards 

 on either side of the crop, and divides into fine branches dis- 

 tributed to the crop and gizzard. About the middle of its course 

 the recurrent nerve is connected with two pairs of small ganglia 

 from which nerves run forward to the supracesophageal ganglion. 



The reproductive organs are somewhat complicated. In 

 the adult male the testes are no longer functional, and are with 

 difficulty distinguished from the fat body in which they are 

 imbedded. In the young males, however, they can be readily 

 discovered as two groups of small spherical vesicles lying 

 beneath the fifth and sixth abdominal terga on either side of 

 the body, and discharging their contents into two narrow 

 tubular sperm-ducts. The sperm-ducts run backwards as far as 

 the seventh tergum, and then turn forwards and upwards to open 

 into a complex organ of relatively considerable size called the 



