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N. E. McINDOO 



3. Disposition 



In the preceding pages, the structure of the two types of 

 olfactory organs from various parts of the integument has been 

 described, and now the distribution and number of them may be 

 discussed without one feeling that some of the hair sockets had 

 been mistaken for single olfactory pores. 



a. Single olfactory organs. In all of the adult insects examined 

 by the writer, most of the olfactory pores lie in groups which are 

 tolerably constant in number and in position, but in the larva 



25 



Figs. 23 to 25. External view of compound and single olfactory organs, and 

 olfactory pegs on distal half of last antennal segment. Fig. 23 represents 9 

 compound organs and 3 single ones on ventral side of antenna, viewed from a 

 flat surface, X 100; 2 of the compound organs at extreme tip are not drawn. 

 Fig. 24, represents 6 compound organs, 4 single ones and 1 bunch of olfactory- 

 pegs {Pg) on dorsal side of antenna, viewed from a fiat surface, X 100. Fig. 25 

 shows external structure of a compound and a single organ, X 320; the small 

 circles represent pore apertures. 



