360 THE LOCUST 



ganglion is to be correlated with its innervation of the metathoracic 

 legs. Since it also sends nerves to the auditory organs, which 

 are located in the first abodminal segment, and since there is no 

 pair of ganglia corresponding to this segment in the abdomen, it is 

 probable that this third ganghon of the thorax is actually the 

 third thoracic and the first abdominal pair of ganglia of the embryo, 

 fused to form a single large ganglionic mass with many nerves. 



In the abdomen of the adult there are five ganglia. These, how- 

 ever, represent fusions of paired embryonic ganglia, particularly 

 at the posterior end. The primitive arrangement, in which there is 

 a pair of ganglia in each segment of the body is, therefore, indicated 

 in this region as in the head and thorax. The nervous system of the 

 grasshopper is composed in the fashion typical for arthropods 

 and annulates, and the correspondence between the number of 

 ganglia and the number of segments in thorax and abdomen is 

 tolerably certain. In some adult insects and in many insect 

 larvse the antero-posterior fusions of ganglia are less developed 

 than in the locust. In others there is a more specialized relation- 

 ship, but even in such instances the system can usually be traced 

 to paired ganglia corresponding to the somites in the embryo. 

 The nervous system and the appendages are thus the two most 

 important systems of organs through which Hght is thrown upon 

 obscurities in the metamerism. 



Sense-organs and Behavior. — The locust, like the majority 

 of insects, is well equipped with sense-organs. The sense of 

 touch is distributed over the entire surface of the body, although 

 the antennae, mouth parts, cerci at the posterior end of the abdo- 

 men and the distal segments of legs are particularly sensitive {cf. 

 Fig. 182 Left). The seat of the sense of taste (cf. Fig. 182 Center), 

 which is a median area on the anterior face of the labium or second, 

 pair of antennae, has been mentioned in the description of these 

 appendages. Although the antennae are primarily tactile organs, 

 the sense of S77iell appears to be located in their basal region, as 

 may be demonstrated by testing the reactions to odors and then 

 coating the antennae with paraffin (cf. Fig. 182 Right). In some 

 insects, such as the moths, this sense must be highly developed, 

 since the males will " come up against the wind " for long dis- 

 tances in search of the females. The greater development of the 

 antennary hairs of the male moth and the fact that the males 

 are unable to find the females when deprived of their antennae 



