398 



THE INVERTEBRATA 



transverse commissures. The anterior three pairs of gangHa of the 

 ventral chain are always fused to form the suboesophageal ganglion, 

 the nerves from which supply the mouth parts. The suboesophageal 

 ganglion is united by paraoesophageal connectives to the brain. 



The brain consists of three pairs of closely fused ganglia which 

 supply the eyes, antennae and labrum respectively (see p. 382). 



Fig. 298. Nervous system of a grasshopper. After Uvarov. A, Ventral 

 chain. B, Brain and associated nerves. C, Optical section through head. 

 ann. antennary nerve and ganglion; dc. deutocerebrum ; ocn. ocellar nerve; 

 op.ga. optic ganglion ; pc. protocerebrum ; sug. suboesophageal ganglion ; syg. 

 sympathetic ganglia; tc. tritocerebrum. 



In addition to this is the sympathetic system (Fig. 298 B, C) which 

 supplies the muscles of the alimentary canal and of the spiracles. 



Metamorphosis. Insects, like all other arthropods, attain their 

 maximum size by undergoing a succession of moults or ecdyses. The 

 number of moults which an insect passes through is fairly constant 

 for the species, and the form assumed by the animal between any 



