INSECTS 



Gng-V- - 



Gng-VTI 

 Gng-vm 



, -Proc 



~vm 

 tx 

 x 



Fig. 72. The general nervous system of a grass- 

 hopper, as seen from above 

 Ant, antenna; Ao, aorta; fir, brain; Or, cercus; E, 

 compound eye; Gng/, ganglion of prothorax; 

 Gng2, ganglion of mesothorax; Gngj+I+Il+III, 

 compound ganglion of metathorax, comprising 

 the ganglia belonging to the metathorax and the 

 first three abdominal segments; GnglV — GngVIH, 

 ganglia of the fourth to eighth abdominal seg- 

 ments; 0, ocelli; Proc, proctodeum, or posterior 

 part of alimentary canal; Sa, suranal plate; 

 Stgll — X, second to tenth segments of abdomen; 

 SoeGng, suboesophageal ganglion; Stom, stomo- 

 deum, or anterior part of alimentary canal 



stimulus, most like- 

 ly, comes from the 

 products of physio- 

 logical changes be- 

 ginning to take place 

 in the body that will 

 soon result in the 

 transformation of 

 the caterpillar into 

 a chrysalis, a stage 

 when the insect 

 needs the protection 

 of a cocoon. These 

 activities of insects 

 we call instincts, but 

 the term is simply a 

 cover for our ignor- 

 ance of the processes 

 that cause them. 



External stimuli 

 are things of the 

 outer environment 

 that affect the living 

 organism. They in- 

 clude matter, elec- 

 tromagnetic energy, 

 and gravity; but the 

 known stimuli do 

 not comprise all the 

 activities of matter 

 or of the "ether." 

 The common stimuli 

 are: pressure of 

 solids, liquids, and 

 gases; humidity; 

 chemical qualities 

 (odors and tastes); 



I 120 



