1914.] natural sciences of philadelphia. 549 



7. Discussion. 



A discussion of all the literature available pertaining to the scent- 

 producing organs of insects has been prepared, but since such a 

 long discussion cannot be presented here, only a brief outline will 

 l)e given. 



A review of the literature shows that the substance produced by 

 any scent -producing organ is secreted by unicellular glands which 

 as far as known are modified hypodermal cells. For description, 

 scent-producing organs may be divided into five types based on their 

 devices for disseminating the odor and for storing the secretion as 

 follows: (1) No special device for disseminating the odor or storing 

 the secretion; (2) gland cells associated with hairs and scales as a 

 means of scattering the odor more effectively; (3) ''evaginable" 

 sacs lined with hairs connected with gland cells as a device for storing 

 and distributing the odor; (4) articular membranes serving as 

 pouches for storing and preventing a too rapid evaporation of the 

 secretion; (5) specialized tubes and sacs acting as reservoirs for 

 storing and discharging the secretion. 



The first type is the simplest of all five types. It is best repre- 

 sented as unicellular glands uniformly distributed over the entire 

 body surface as found in some beetles (Tower, 1903). In the beetles 

 Dytiscus and Acilius unicellular glands lie just beneath the hypo- 

 dermis between the head and tergite of the prothorax (Plateau, 1876). 

 In the blister beetle, Meloe, are found unicellular glands beneath 

 the hypodermis on both sides of the femoro-tibial articulations 

 (Berlese, 1909). These gland cells are similar in structure to those 

 of the honey bee. Beneath the femoro-tibial articulation in Cam- 

 ponotus and the tibio-tarsal articulation in Formica, Schon (1911) 

 found unicellular glands. Beneath the hypodermis of the caruncles 

 of the Indian roach, Corydia, lie unicellular glands, also similar to 

 those of the bee (Klemensiewicz, 1882). In this type of scent- 

 producing organ the secretion passes through the chitinous tubes 

 to the exterior where it spreads over the surface of the' chitin sur- 

 rounding the exits of the tubes. 



In regard to spreading the secretion over a wider area, the secontl 

 type is much more highly developed than is the first type. This is 

 accomplished in most cases by the secretion spreading over the 

 surfaces of many large hairs arranged in tufts which may be expanded 

 into a fan-shaped figure. The hind tibiae of the male moth Hepialus 

 hecla are greatly swollen and are almost filled with large unicellular 



