.Chap, i.] THE NEEVOTJS SYSTEM IN THE ZOOLOGICAL SERIES. 365 



mass, sometimes connected by fibrous commisstires, sometimes 

 joined together direct. From the inferior ganglion go forth two 

 abdominal cords directed from the front to the back, and bearing 

 each a series of ganglions, whence radiate nervous threads. The 

 ganglions of each cord usually face each other, and thus form, by 

 their juxtaposition, pairs of nervous centres of which each corre- 

 sponds to a segment of the body (Fig. 57). If many segments 



/- --» 



Fio. 57. 



A, B. C, Nervous Systems of Insects. 

 ■i, termites; B, eoleopter (dyHscnis) ; C, fly; gs, oesopbagian ganglion superior (cerebroidal 

 ganglion) ; gi, oesophagian ganglion inferior ; gr, g^, g3, nnited ganglions of the ventral 

 chain; o, eyes. 



blend together in the course of the development, the correspond- 

 mg nervous ganglions do the same, and thus constitute a more 

 important nervous mass.^ 



■ The more voluminous of the ganglions is the more anterior of 



the super-oesophagian ganglion. It is called cerebral or cerebroidal 



* Gegenbaur. loc, cit. 



