STRUCTURE 541 



already described, though Kiinckel came to the conclusion that 

 the saliva when placed in living plants is totally innocuous. 1 



The ganglia of the nervous system are all concentrated in 

 the thorax and head. In some cases (in various Homoptera) the 

 infra-oesophageal ganglion is placed at a distance from the supra- 

 oesophageal ganglion, and may even be united with the thoracic 

 mass of ganglia (Orthezia, etc.) ; in this case the chitinous frame- 

 work of the mouth-parts is interposed between the supra- and 

 the infra-oesophageal ganglia. In Pentatoma all the three gan- 

 glionic masses are brought into close proximity, but in Nepa the 

 thoracic mass of ganglia and the infra-oesophageal ganglion are 

 widely separated. 



The ovarian tubes vary greatly in number : according to List 

 in Orthezia cataphracta the number differs considerably in dif- 

 ferent individuals, and even in the two ovaries of the same 

 individual, the number being usually two. The testes are not 

 placed in a common tunic, though they are frequently approxi- 

 mated or even contiguous. 2 



The smell of bugs is notorious. In many species it is not 

 unpleasant, though as a rule it is decidedly offensive. It is a 

 remarkable fact that the structures connected with the production 

 of this odour are different in many cases in the young and in 

 the adult. The odour emitted by the latter proceeds from a sac 

 seated at the base of the abdomen, and opening exteriorly by 

 means of an orifice on each side of the metasternum ; while in 

 the young there are two glands situated more dorsally and a 

 little more backwards, and opening on two of the dorsal plates 

 of the abdomen (Fig. 255, A). 3 In the young the dorsum of the 

 abdomen, where the stink-glands open, is exposed, but this part 

 in the adult is covered by the wings. The odorific apparatus is 

 specially characteristic of Heteroptera, and Kiinckel states that 

 there is so much variety that generic and even specific characters 

 might be drawn from conditions of the stink-glands. As a rule 

 they are most constantly present in the plant-feeding forms ; in 

 some essentially carnivorous forms (Eeduviidae, Nepidae, Xoto- 



1 Ann. Soc. ent. France (4) vii. 1867, p. 45. 



2 The chief work on the internal anatomy of Hemiptera is still Dufour's He- 

 cherches anatomiqucs et physiologiques sur les Htmipteres, Mem. Savans Grangers, 

 Paris, iv. 1833, p. 129. 



3 Kiinckel, Ann. Soc. ent. France (4) vii. 1867, p, 45, and C.R. Ac. Paris, cxx. 

 1895, p. 1002. 



