NO. 8 MORPHOLOGY OF INSECT SENSE ORGANS SNODGRASS 4/ 



form organs the cone is not present, or at least has not been distin- 

 guished by those who have described and figured the organs. When 

 present, it is perforated by a central opening or by an axial slit, 

 through which the distal end of the sense cell process (d) is inserted 

 on the under surface of the outer lamella. Beneath the cone is the 

 usual canal in the cuticula, which does not differ from that of the 

 sensory hairs. 



The innervation of the campaniform organs is always through a 

 single sense cell (fig. 21, SCI). The sense cell is usually large, oval 



Do SR 



Mm Nv 



Fig. 21. — Structure of a campaniform sensillum (diagrammatic from 

 Sihler, 1924, organ on cercus of Pcrihlaueta oricntalis) . 



Cuticular canal beneath dome occupied by a single cell {CI), ap- 

 parently the trichogenous cell (fig. 13 B, ECl) ; no cap cell (mem- 

 brane cell) shown in this organ. 



or fusiform ; it lies within the hypodermis but may project below the 

 general level of the basement membrane. In some organs the distal 

 process {d) appears to end directly on the inner surface of the outer 

 lamella of the dome, but in most of them there is a typical sense rod 

 {SR) at the end of the process. 



The other cells of the campaniform sensillum have not been defi- 

 nitely identified with those of the hair-bearing sensilla. Erhardt 

 (1916) notes the presence of enveloping cells associated with the 

 sense cell in the campaniform organs of the wing basis of CJirysopa. 

 Vogel (1911) finds two enveloping cells in the organs of the wing 

 bases of Lepidoptera, but he says their boundaries are not distinct. 



