58 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 82 



molitor, and also with all the small hairs on the labial palpi of the 

 last species. The present writer (46) found tactile hairs on the cotton 

 boll weevil as follows: Sense hairs (Sensilla trichodea) on the head 

 capsule, antennae, mouth parts, thorax, legs, wings and abdomen ; 

 sense bristles (S. chaetica) on nearly the same parts; and sense pegs 

 (S. basiconica) on the head capsule, mouth parts, and genitalia. 



In regard to tactile hairs on the Mexican bean beetles, all parts of 

 the integument were not searched for them, but practically all the 

 innervated hairs already discussed might be considered as touch 

 hairs; however, the sense hairs (Sensilla trichodea) are considered 

 to have no function other than that of touch. On the base of each 

 antenna lie two groups of these hairs (figs. 6, B, and 15, J, St) and 

 each trochanter bears one or two groups (fig. 9, C, and 15, H, St). 

 They were also found on the maxillary and labial palpi (fig. 15, I, St) 

 of the adult and on the head (fig. 16, C, St) of the larva. 



C. Scent-Producing Organs and Reflex " Bleeding " 



The study of scent-producing organs follows as a corollary to that 

 of tropisms and sensory receptors, and reflex " bleeding " is closely 

 related to them. Since the sense of smell is such an important means 

 of communication among insects, it is probably true that all insects 

 have structures for producing odors. In fact these structures have 

 already been described for most insect orders, and particularly for 

 Coleoptera. 



The writer (43) in 1917 reviewed the literature on this subject. 

 A brief summary of that review concerning beetles follows : The 

 simplest type of a scent-producing organ in beetles is composed of 

 unicellular glands distributed over the entire body surface. In some 

 beetles these unicellular glands are grouped and thus form glands 

 varying considerably in complexity. In Malachins two pairs of car- 

 uncles serve as the scent-producing organs ; unicellular glands lie in 

 the walls of these structures. In Dytiscus, Gyrinus, and Acilius two 

 different kinds of liquids issue from unicellular glands situated in the 

 articular membranes between the thoracic segments. The liquid 

 emitted at the femoro-tibial articulation during reflex " bleeding " of 

 certain beetles seems to be secreted by two types of unicellular glands 

 at this location. The highest type of scent-producing organ among 

 insects is the anal glands of beetles. These have been found in several 

 families. 



In regard to the Mexican bean beetle, no careful search was made 

 for the purpose of finding scent-producing organs other than the 



