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SMITHSONIAN MISCELLANEOUS COLLECTIONS 



VOL. 



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mass. The first pair of ganglia constitutes the profoccrcbruin (fig. 

 4, iBr), the second the deutocerebrum (2Br), and the third the 

 fritoccrcbrum (jBr). The transverse commissures of the first and 

 second pair form fibrous tracts (iConi, 2Com) within the brain, 

 but the connectives of the tritocerebral gangha {jConi) form an 

 independent commissure beneath the oesophagus {CE). The trito- 

 cerebral ganglia, therefore, really belong to the post-oral series of 

 ganglia. 



Fig. 4. — Diagrammatic structure of brain and suboesophageal ganglion. 



The brain consists of the protocerebral (iBr), deutocerebral {2Br), 

 and tritocerebral ganglia (jBr), the first two connected by transverse 

 commissures (iCom and 2C0111) above the oesophagus, the third by a 

 commissure {3C0U1) beneath the oesophagus. The suba?sophageal 

 ganglion {SocGng) consists at least of the united fourth, fifth and 

 sixth head ganglia, with nerves to the mandibles, maxillae, and labium, 

 and with other nerves from its posterior part (not shown). 



In the brain, the same essential elements are to be found that 

 are present in the ganglia of the ventral cord, except that in it 

 cells of longitudinal commissural fibers have not been distinguished 

 as such. The internal structure of the brain, however, in the higher 

 insects, is far more complicated than that of a ventral ganglion, 

 first, because of the composit nature of the brain, second, because 

 of the presence of the great sensory tracts of the eyes and the an- 

 tennae, and third, on account of the development of the corpora 

 pcdunciilata, or so-called mushroom bodies, in which there come 



