46 



SMITHSONIAN MISCELLANEOUS COLLECTIONS 



VOL. JJ 



form, organs, as used in a general sense by Berlese (1909), is here 

 selected for euphony and because in descriptive value it is equal to 

 any of the others. 



The external parts of the campaniform organs are, in most cases, 

 small, rounded, dome-like papillae or but slightly convex swellings, 

 usually less than 25 microns in diameter ; but sometimes they are 

 reduced to minute discs, slightly sunken in the outer surface of the 

 body wall, having the appearance of hair follicles from which the 



Fk;. 20. — Various types of campaniform organs, vertical sections 

 through cuticular parts and ends of sense cell processes with sense rods. 



A, Diagrammatic structure of a typical organ : a, outer lamella of 

 dome; h, inner lamella, the cone or cushion; d, distal process of sense 

 cell with axial fiber ending in the sense rod (SR). 



B, organ from base of halter of Calliphora (Pflugstaedt, 1912) : c, 

 attachment plate of sense cell process. C, longitudinal section of same. 

 D, dorsal scapal organ of halter of Syrphus (Pflugstaedt). E, from 

 cercus of Periplancta ainericana (Sihler, 1924). F, sunken organ on 

 labium of Dydscus (Hochreuther, 1912). G, snnken organ with no ap- 

 parent external opening, on mandible of Dytiscus (Hochreuther). 



hairs have been removed, though they are usually distinguishable 

 from the circular hair sockets by a more elliptical or oval form. 



The dome or disc in typical examples usually consists of a thin, 

 outer, imperforate lamella of dense chitin (fig. 20 A, a), and of an 

 inner layer of clear softer chitin (b). These two parts probably be- 

 long to the epidermal and dermal layers, respectively, of the body 

 wall cuticula (Epd and Dm). In stained specimens the appearance 

 is sometimes reversed because the softer inner layer, according to 

 most writers, colors more darkly in ordinary staining reagents. Tlie 

 inner layer is the cushion (Polstennassc) of German writers, the 

 cone of Mclndoo (1914). Usually it has the form of a cone or an 

 inverted cup or saucer beneath the outer lamella. In many campani- 



