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ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 2 8 



insects which follow scented trails this secondary use seems especially 

 probable. The adhesive-secreting glands lie in the soft pads on the 

 underside of the feet, and are usually connected with small hairs, 

 called tenent hairs (k). These hairs are hollow and are usually 

 open at their tips ; through them the sticky secretion from the glands 

 is forced to the exterior, where under certain conditions it may be 

 seen as fine threads. This example shows how scented trails may 

 possibly be made by the feet of insects in much the same way as 

 scented tracks are made by dogs, the sweat glands in the pads of 

 the dogs' feet seeming to deposit an odorous material wherever a 

 dog steps. Ants and termites have been observed to lay down scented 

 trails by depositing tiny specks of material from the tip ends of their 

 abdomens, and thereafter they follow these tracks. 



Figure 4. — Diagrams showing locations of scent glands of insects. A, superficial 

 view of a portion of an elytron or wing cover of a cotton boll weevil, showing 

 large hairs (h) and widely scattered gland pores (p). B, cross section through 

 tarsus or foot of a beetle, showing nerves (n) running to touch hairs (t) and 

 gland cells (<;) which, when stimulated, force their sticky secretion through open- 

 ings in numerous hairs (h) on the "soles" of the feet. (From Packard, after 

 Dewitz. ) C, front leg of a male moth, showing the fan-shaped group of scent 

 hairs (s). (From Schroder, after Illig.) D, female of the silkworm moth, show- 

 ing the evcrsible sacs (s) as scent-producing organs. (From Schroder, after 

 Freiling. ) E, larva of a swallow-tail butterfly, showing eversible sacs or osma- 

 terium (s). which emit a defensive odor. (After Berlese) 



Scent glands of a second type include peculiarly arranged tufts 

 of long hairs, on the legs and elsewhere, on male moths (fig. 4, C, s). 

 The secretions from all these organs have been credited with purposes 

 of allurement and are supposed to attract the opposite sex. They 

 have been regarded as aromatic, volatile oils. Their odors usually 

 are to man very agreeable indeed, and have been described as 

 resembling many of our most pleasing scents, even including those 

 from some of our fancy perfumes. As a rule, each species of insect 

 has its own characteristic odor. 



In the case of a third type of scent glands, eversible sacs or 

 pouches, usually lined with tiny hairs which connect with the glands, 

 serve as special devices for storing the secretion and distributing 

 the odors. With some species the odors from these glands serve 



