FUSION OF THE VENTRAL GANGLIA 



225 



ganglia, and usually from five to eight pairs of ganglia in the 

 abdomen. 



In certain winged insects the process of fusion or degeneration 

 is carried to such an extreme that there are either no abdominal 

 ganglia (Fig. 242, Z>), or their vestiges are situated in the thorax 

 and partially fused with the thoracic ones, as in the May beetle, in 

 which the prothoracic pair of ganglia is separate, while the two 

 other thoracic ganglia are fused with the abdominal, the latter being 

 situated in the thorax; this fusion is carried to a further extent 



FIG. 248. Nervous system of the May bee- 

 tle, Lachnosterna fusca : w 1 , nerve to 1st, 



?e 2 , nerve to 2d, pair of wings ; ig, inFracesopha- separate abdominal ganglia, 

 geal ganglion. 



FIG. 244. The same of the stag-beetle, Lu- 

 canus dania, where there are 3 thoracic, and 8 



than in any other Coleoptera yet examined. In many Diptera and 

 Hemiptera the abdominal ganglia are either absent or the vestiges 

 are fused with the thoracic ganglia. 



Rhizotrogus, which is allied to our May beetle, as also Hydrometra 

 and the Stylopidts are said to lack the suboesophageal ganglion 

 (Brandt). 



In numerous Coleoptera (Acilius, Gyrinus, Necrophorus, Melo- 

 lontha, Bostrichus, Rhynchsenus) ; in many Diptera (Culex, Tipula, 

 Q 



