44 



SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I42 



glion, therefore, is actually a preoral first ganglion of the ventral 

 nerve cord, as becomes evident if the tritocerebral ganglia are im- 

 agined to be restored to their primitive ventral postoral position 

 (fig. 20). In the symphylan Hanscniclla the frontal ganglion is shown 

 by Tiegs ( 1940) to be represented by a pair of ganglia connected by a 

 preoral commissure. Nerves go to the clypeolabrum from the ganglia, 

 and the stomodaeal recurrent nerve arises from the commissure. 



I II III IV 



Clp— ' 

 frGng" 



Lrn prrndGng-TTidGng- 



Fig. 20. — Diagrammatic theoretical reconstruction of the anterior region of a 

 primitive arthropod before the postoral segments (I-IV) became a part of the 

 head. The premandibular ganglia (future tritocerebral ganglia) are still ventral 

 behind the mouth. The preoral frontal ganglion (frGtig) is seen to be the first 

 ganglion of the ventral nerve cord, innervating the clypeal and labral muscles, 

 and the ectodermal stomodaeum. 



The connection of the preoral frontal ganglion with the pre- 

 mandibular tritocerebral ganglia is of no more significance than the 

 connection of these ganglia with the mandibular ganglia or the union 

 of any other consecutive ganglia in the ventral nerve cord. As de- 

 scribed by Orlov (1924) in the larva of Oryctes na^icornis the fron- 

 tal ganglion is in itself a fully developed nerve center containing 

 sensory, motor, and association neurons. The preoral ocular and 

 antennal brain centers are primitively supraoesophageal ganglia con- 

 nected with the ventral nervous system by way of the postoral trito- 

 cerebral ganglia. 



Considering the difficulties encountered by theories that attempt 



