634 



THE SENSES AND SENSORY ORGANS. 



The setae are on an average o'i mm. in length, and each 

 apparently receives a process from one of the subjacent 

 ganglion cells. A layer of small cells lies immediately beneath 

 the cuticle, and these apparently send processes into the bases 

 of the setae. The deeply-seated position of this organ in a small 

 pouch on either side of the front of the prosternum renders it 





FIG. 85. A highly magnified section of a part of the prosternal organ ; g, ganglion 

 cells; //, hypodermal cells; n, nerve; s, transparent setce. 



most improbable that it is a tactile organ, and its setae present 

 a similarity to the large olfactory setae in the sacculi on the 

 antenna, which is very striking, although they are twice as long. 

 Further observations are needed to throw light upon the nature 

 of this most puzzling organ. 



