584 THE SENSES AND SENSORY ORGANS. 



The following special sensory organs have been described : 



1. Special sensory setae intermixed with ordinary tactile and 



protective bristles ; Krapelin. 



2. Olfactory cones (Riechkolben) ; Lcydig, Ford, ami Lub- 



bock (PI. XLL, Fig. 2, C). 



3. Simple pits containing a filiform hair ; Lubbock. 



4. Simple pits containing a papilla ; Erichson. 



5. Champagne-cork organs ; Ford. 



6. Complex cones ; Hauser. 



7. Stethoscope-like organs ; Ford and Lubbock. 



8. Tympanules ; Hicks. Simple pits ; Krapelin. 



9. Setiferous sacs or canals ; Krapelin (PL XLL, Fig. 2, B). 



The first five of these are figured by Krapelin, and, although 

 he regards them all as modified setae, I think he has disregarded 

 a very important fact the deciduous character of the special 

 sensory setae of the antennas. I have observed all the appear- 

 ances in the antenna of the Blow-fly, but they result from the 

 true setae having been detached, leaving more or less of their 

 bases and contents attached to the antennae. Very commonly 

 a flame-shaped process, or protoplasmic cone, or only the 

 naked axis cylinder remains. Where the base of the seta is 

 sunk beneath the surface, a projecting ring of chitin is left in 

 the pore canal, giving rise to the champagne-cork-like organ 

 of Forel. 



With regard to the complex cones of Hauser, Krapelin was 

 unable to find anything like them, although he sought for 

 them in the insects in which Hauser described them. They 

 are apparently the same thing as the stethoscope-like organs 

 of Forel. In the mature insect it is often very difficult, where 

 the antennae are very hard, as in the Hymenoptera, to obtain 

 sections; hence immature insects, or even nymphs, have been 

 used. 



In the Blow-fly nymph the sensory setae of the antennas 

 are developed in follicles, and their bases closely resemble the 

 bulb of the stethoscope-like organs of Forel. I am inclined 

 to n-^.ird these as partly developed sensory setae ; as, how- 



