NERVOUS SYSTEM. 



81 



At a higher stage of development a circum-pharyngeal nerve ring 

 is developed. With the commencing segmentation of the body the 

 number of ganglia increases, and in addition to the brain there is 

 present a ventral nervous system consisting either of ventral cord 



fl'- G 



FIG. 76. Alimentary canal and 

 nervous system of Mesosto- 

 mum Ehrenbergi (after Graff). 

 G, the paired cerebral ganglia 

 with two eye-spots; St. one 

 of the two main lateral nerves ; 

 Z>,alimentary canalwith mouth 

 and pharynx. 



FIG. 77. Nervous system of FIG. 78. Nervous system 



the larva of Coccinella 

 (after Ed. Brandt). G, an- 

 pra-cesopfcageal ganglion 

 or brain; Gfr, frontal 

 ganglion ; Sg, suboeso- 

 phageal ganglion ; Q-',-G", 

 the eleven ganglia of the 

 rentral chain of thorax 

 and abdomen. 



of adult Coccinella (after 

 Ed. Brandt). Ag, optic 

 ganglion. The other let- 

 ters as in fig. 77. 



(Gephyrea) or of a ventral chain of ganglia, which may have a 

 homonoinous (Annelids) or heteronomous (Arthropods) arrangement 

 (figs. 77 and 78). The concentration of the nervous system begun 



6 



