NO. 8 MORPHOLOGY OF INSECT SENSE ORGANS^SNODGRASS * 3/ 



The sense rods of the chordotonal organs have been carefully 

 studied in many different insects. They are often specifically called 

 scolopalcc, but there is no reason for distinguishing scolopal?e from 

 sense rods in general, or for limiting the term to the chordotonal 

 rods. The scolopalse of one of the chordotonal organs in the base of 

 the halter of Diptera are described by Pfiugstaedt (1912) as attached 

 to the cuticula, each by a long terminal fiber (fig. 15 E, t) formed by 

 a continuation of the ribs of the scolopala walls. Vogel (1912) finds 

 each rod in the chordotonal organs of the wing bases in Lepidoptera 

 likewise attached to the cuticula by a long terminal filament (lig. 15 F, 

 t). In some chordotonal organs there is a vacuole in the sense cell 

 process at the base of the scolopala (fig. 15 G, Vac), which is tra- 

 versed by the axial fiber {AxF). This vacuole should not be con- 

 fused with the vacuole of the basal enveloping cell, which contains 

 the distal process of the sense cell. 



The structure of the sense rods in the tympanal chordotonal 

 organs of Orthoptera has been particularly studied by Schwabe 

 (1906). Each scolopala of the sensory body attached to the inner 

 surface of a grasshopper's " ear " (fig. 27 B, SB) is a minute hollow 

 rod, about 23 microns in length, fusiform, pointed at the distal end, 

 slightly tapering proximally (fig. 15 H, I). Stained specimens, ex- 

 amined under high magnification, show that the walls of the rod 

 are marked by longitudinal ribs (r) formed by thickenings on the 

 inner surface (J, K, L). On the distal two-thirds of the scolopala 

 there are ten ribs, each enlarged at its middle ; but proximally the 

 ribs unite in pairs, forming five thicker ridges on the basal third of 

 the rod. The head of the scolopala is occupied by a dark-staining 

 apical body (H, I, J, AB) to which is attached the end of the axial 

 fiber (H, AxF) from the sense cell. In the rods of the chordotonal 

 organs of Cerambycid larvae, Hess (1917) finds seven ribs on the 

 basal part that fork to form 14 on the distal part. Vogel (1923 a) 

 says that the ribs of the chordotonal rods of the cicada appear to be 

 on the external surfaces of the rods. 



In the chordotonal organs, the sense rods are usually some dis- 

 tance removed from the cuticula, being situated in the outer end of 

 the enveloping cell or partially in the base of the elongate cap 

 cell (fig. 26, SR). They are usually connected with the cuticula, 

 as we have seen (fig. 15 E, F), by a long terminal filament {t) tra- 

 versing" the cap cell, but in some cases the connection appears to be 

 lost. Thus, as noted by Schwabe (1906) in the tympanal organs of 

 the Orthoptera, and by Hess (1917) in the chordotonal organs of 

 Cerambycid larvae, the terminal fiber, if present, is continued from 



