THE OLFACTORY SENSE OF COLEOPTERA. 45 1 



DISCUSSION. 



Since the writer ('14c) has already written a complete review 

 of all the literature available concerning the sense of smell in 

 insects, only a brief discussion is necessary in this paper. 



Hicks ('57) says that the olfactory pores in Coleoptera are 

 arranged in long rows along the subcostal nerves. The same 

 author ('59) states that in Coleoptera these organs are highly 

 developed and occur in numerous groups on the subcostal vein, 

 mostly at the widest part, but are also scattered along it to the 

 fold of the wing. In Carabus they are found on veins other than 

 the subcostal. In many beetles the pore is overarched by a hair, 

 which probably protects the organ. He could distinguish no 

 sexual differences in these organs, except the pores are slightly 

 larger in the females, due to their greater size. Hicks ('60) 

 first found the olfactory pores on the legs of beetles. The 

 present writer has never seen a hair overarching an olfactory pore. 



Hochreuther ('12) seems to be the first to study the internal 

 anatomy of the olfactory pores in beetles. Since he used only 

 Dytiscus marginalis and perhaps because he did not have enough 

 sections through these organs, he failed to understand their 

 anatomy. He states that each dome-shaped organ is located at 

 the bottom of a chitinous flask, the mouth of which communicates 

 with the exterior. Instead of the peripheral end of the sense 

 fiber coming into direct contact with the air in the flask, it 

 apparently stops just beneath the chitinous dome at the top of 

 the organ. His terminal strand (Terminalstrand) may be the 

 same as the hypodermal secretion forming the cone described 

 by the writer. Hochreuther found a few of these dome-shaped 

 organs on the epicranium near the margin of the eyes, nine on the 

 proximal end of the first antennal segment, two on the distal end 

 of the second antennal segment, a few on the dorsal side of the 

 labrum, a very few on the dorsal side of the mandible, several 

 on each maxilla, about 18 on the first four segments of the front 

 legs, about 10 on the first tfiree segments of the middle legs, and 

 a few on the trochanters of the hind legs. He evidently did not 

 examine the wings. Thus according to Hochreuther these 

 organs are rather widely distributed. Since the peripheral ends 

 of the sense fibers do not come into contact with the outside air. 



