94 ENTOMOLOGY 



The thoracic ganglia govern the appendages of their respec- 

 tive segments. These ganglia and those of the abdomen are 

 to a great extent independent of brain control, each of these 

 ganglia being an individual motor center for its particular 

 segment. Thus decapitated insects are still able to breathe, 

 walk or fly, and often retain for several days some power of 

 movement. 



In regard to the sympathetic system, it has been shown ex- 

 perimentally that the frontal ganglion controls the swallowing 

 movements and exerts through the stomatogastric nerve a 

 regulative action upon digestion. The dorsal sympathetic sys- 

 tem controls the dorsal vessel and the salivary glands, while 

 the ventral sympathetic system is concerned with the spiracu- 

 lar muscles. 



5. SENSE ORGANS 



For the reception of sensory impressions from the external 

 world, the armor-like integument of insects is modified in a 

 great variety of ways. Though sense organs of one kind or 

 another may occur on almost any part of an insect, they are 

 most numerous and varied upon the head and its appendages, 

 particularly the antennae. 



Antennal Sensilla. Some idea of the diversity of form 

 in antennal sense organs may be obtained from Figs. 116-125, 

 taken from a recent paper by Schenk, whose useful classifica- 

 tion of antennal sensilla, or sense organs, is here outlined : 



1. Sensillum cceloconiciim a conical or peg-like projection 

 immersed in a pit (Figs. 116-117). In all probability 

 olfactory. 



2. 5*. basic onicum a cone projecting above the general sur- 

 face (Fig. 118). Probably olfactory. 



3. S. styloc ' onicum a terminal tooth or peg seated upon a 

 more or less conical base (Fig. 119). Olfactory. 



4. S. chceticum a bristle-like sense organ (Fig. 120). 

 Tactile. 



5. 6\ trichodeum a hair-like sense organ (Figs. 121, 122). 

 Tactile. 



