224 



TEXT-BOOK OF ENTOMOLOGY 



than in vertebrates the entire nervous system, and not the brain 

 alone, is the organ of the mind of insects. 



The simplest, most primitive form of the nervous system of insects 

 is seen in that of the Thysanura. That of Cainpodea has not yet 

 been fully examined, but in that of the more complicated genus, 

 Machilis (Fig. 239), we see that there is a pair of ganglia to nearly 

 each segment, while the brain (Fig. 241) is composed of three lobes, 

 viz. the optic, the cerebral (Fig. 239, g), behind which is the antennal 

 lobe, from which the antennal nerve takes its origin. Behind the 

 opening for the throat (oe) is situated the first ganglion of the 

 BCD 



PIG. 242, A-D. The nervous systems of 4 genera of Diptera, to demonstrate their various 

 degrees of fusion of ganglia: A, non-concentrated more primitive nervous system of Chironomus 

 plumosu/i, with 3 thoracic and 6 abdominal ganglionic masses. B, nervous system of /,'/;<///* 

 steroorea, with 2 thoracic and 5 abdominal ganglionic masses. C, nervous system of Tiilniiiiix 

 bovin-UK, with 1 thoracic ganglionic mass, and the abdominal ganglia closely approximated. 

 D, highly modified nervous system otSarcophaga carnarSo. in which all the ganglia of the ventral 

 cord behind the suboesophageal ganglion are fused into a single ganglionic mass. After Brandt, 

 from Lang. 



ventral cord, the suboesophageal ganglion, which gives rise to 

 the nerves supplying the jaws and other mouth-parts. 



In the Collembola, which are retrograde Thysanura, there are from 

 one (Smynthurus), to three or four ventral ganglia. 



In the winged insects, where the ganglia are more or less fused, 

 the fusion taking place in the head and at the end of the abdomen ; 

 there are in the more simple and generalized forms, such as Ephemera, 

 the grasshopper, locusts (Fig. 240), etc., thirteen ganglia besides the 

 two pairs of compound ganglia in the head, three pairs of thoracic 



