48 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 81 



Much experimental work on various temperatures, particularly as 

 control measures, has been done on Lepicloptera, but little or none of 

 it can be discussed from the tropic point of view. The sense of 

 temperature is probably well developed, although in insects, as in our- 

 selves, there are probably no special thermoreceptors. The subhypo- 

 dermal nerve plexus, if present in adult Lepidoptera as found in 

 caterpillars by Hilton (34), could easily perform this function. 

 Humidity, which is closely related to temperature, also has much to 

 do with the behavior of Lepidoptera. Hering (32, p. 201) remarked 

 that butterflies have a barometric sense, because sultriness and low 

 barometric pressure have a characteristic effect on both the adults and 

 larvae. He imagined that some of the antennal organs are the recep- 

 tors. Guenther (2/) hazarded the opinion that the " Sinneskuppeln " 

 (olfactory pores) were barometric receptors. 



Prijffer (y/) states that his results and those of Patijaud demon- 

 strate that female moths cannot lure the males from long distances, 

 in spite of evidence shown years ago by Forel, Fabre, and others. 

 He says that the females of Satuniia pyri L., as an example, can 

 attract the males from a distance of not over 50 meters. Noel (68) 

 concluded that neither sight nor smell is sufficient to explain the attrac- 

 tion from long distances. As a hypothesis, he suggested that certain 

 insects emit special waves or rays, resembling X-rays, or the Hertzian 

 waves, or even the N-rays of Dr. Blondlot. He firmly believed that 

 these rays, which have not yet been isolated or verified, really exist 

 and that they are used in distant communication. It has also been 

 suggested that the bushy antennae of certain moths support this theory. 



C. Scent-Producing Organs 



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

 of tropisms and tropic receptors. Since chemotaxis is such an impor- 

 tant 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 in numerous species belonging to most 

 of the insect orders. 



Several years ago the writer (49) reviewed the literature on this 

 subject. A brief summary of that review concerning Lepidoptera 

 follows : Scent scales on the wings constitute the almost universal 

 type of scent-producing organs in male butterflies. Clark (4) has 

 recently reviewed this subject and added much new information. A 

 pair of invaginated sacs located at the ventro-posterior end of the 

 abdomen has been found in certain male butterflies. These sacs are 



m 



