iv SENSES 121 



starting from a small ganglion in the forehead, then connecting 

 with the brain, and afterwards extending along the oesophagus 

 to the crop and proventriculus (Fig. 66). This is usually called 

 the stomatogastric system. The oesophageal ring we have already 

 spoken of. 



By means of these accessory nervous systems all the organs 

 of the body are brought into more or less direct relation with 

 the brain and the ganglionic chain. 



Our knowledge of these subsidiary nervous systems is by 

 no means extensive, and their nomenclature is very unsettled ; 

 little is actually known as to their functions. 



Organs of Sense. 



Insects have most delicate powers of perception, indeed they 

 are perhaps superior in this respect to the other classes of 

 animals. Their senses, though probably on the whole analogous 

 to those of the Vertebrata, are certainly far from corresponding 

 therewith, and their sense organs seem to be even more different 

 from those of what we call the higher animals than the functions 

 themselves are. "We have already briefly sketched the structure 

 of the optical organs, which are invariably situate on the head. 

 This is not the case with the ears, which certainly exist in one 

 Order, the Orthoptera, and are placed either on the front 

 legs below the knee, or at the base of the abdomen. Notwith- 

 standing their strange situation, the structures alluded to are 

 undoubtedly auditory, and somewhat approximate in nature to the 

 ear of Vertebrates, being placed in proximity to the inner face of 

 a tense membrane ; \ve shall refer to them when considering the 

 Orthoptera. Sir John Lubbock considers no doubt with reason 

 that some ants have auditory organs in the tibia. Many 

 Insects possess rod-like or bristle-like structures in various parts 

 of the body, called chordotonal organs ; they are considered by 

 Graber l and others to have auditory functions, though they are 

 not to be compared with the definite ears of the Orthoptera. 



The other senses and sense organs of Insects are even less 



known, and have given rise to much perplexity; for though many 



structures have been detected that may with more or less prob- 



ability be looked on as sense organs, it is difficult to assigna 



1 Zool. Anz. iv. 1881, p. 4f>2. 



LU LIBRARY 



