NERVOUS SYSTEM. INVERTEBRATA . 39 



D. 32. An immature Water- Scorpion (Belostoma) showing the 

 nervous system. In all the Hemiptera the post-oral part 

 of the central nervous system shows a high degree o 

 longitudinal concentration, and in none perhaps more so 

 than in the Water-Scorpions. In this example the sub- 

 oesophageal ganglion lies close to the cerebral, in the pro- 

 thorax ; it is almost contiguous with the prothoracic 

 ganglion, the approximation of the two being evidently 

 due to the forward position of the 1st pair of legs. The meso- 

 and metathoracic ganglia are fused with one another and 

 with the abdominal chain to form a round central thoracic 

 mass from which nerves are given off to the two posterior 

 pair of thoracic limbs and to the abdomen. Owing to the 

 half-macerated condition of the specimen, the component 

 parts of the central thoracic mass are visible as three pairs 

 of opaque centres representing respectively the meso- and 

 metathoracic ganglia and the united ganglia of the 

 abdominal chain. 0. C. 1299 B. 



D. 33. Two specimens of the nervous system of another species 

 of Water-Scorpion (Nepa cinerea). In its main features 

 this system corresponds with that shown in the last speci- 

 men, but the longitudinal concentration is even more 

 marked. In this species the suboesophageal ganglion is 

 completely fused with the prothoracic. In the upper 

 specimen the nervous system is seen isolated ; in the lower 

 in situ. 0. 0. 1299 B a. 



D. 34. The nervous system of a Lepidopterous larva exposed 

 from the dorsal aspect. The cerebral ganglion consists of 

 two small rounded lobes contiguous in the mid-line. It is 

 united around the oesophagus by a pair of short connectives 

 to a ventral chain, composed (as in the great majority of 

 Lepidopterous larvse) of 11 equal-sized ganglia i.e., 

 1 suboesophageal, 3 'thoracic, and 7 abdominal. The sub- 

 oesophageal and prothoracic ganglia are approximated to 

 one another ; but the remainder lie at about equal distances 

 apart in successive segments of the body. The terminal 

 ganglion is distinctly grooved transversely and represents 

 a fusion of two embryonic ganglia. As in the adult, it 



