THE OLFACTORY SENSE OF COLEOPTERA. 423 



conspicuous. It may be darker (Fig. 13, SCNuc) or lighter 

 (Fig. 23, SCNuc) in color than the cytoplasm in the cell. The 

 nucleoli (Fig. 23, SCNuc) are also conspicuous. 



Smaller sense cells may be seen in the sections through the 

 proximal ends of the trochanters and through the proximal ends 

 of the tibiae. These (Fig. 17, SCi) belong to tactile hairs (Fig. 

 17, THr). 



In the sections through the legs and elytra of Epilachna, 

 gland cells (Fig. 17, GIC) are plainly seen in the hypodermis 

 {Hyp). These are equally as large as the olfactory sense cells, 

 but they are quite different in structure. The diameters of the 

 pores of the glands (PorGl) are slightly smaller than those of the 

 hairs (PorHr), and they are much smaller than those of the 

 olfactory pores (For). The morphology and physiology of these 

 gland cells will be given in another paper. 



The shapes of the external ends or tops of the pits depend on 

 the shapes of the pore apertures when seen in superficial views. 

 That is, they are round, oblong, slitlike or clublike. The internal 

 ends or bottoms of the pits are always round. The pore aperture, 

 proper, is the round opening leading from the bottom of the pit 

 to the external end of the pore. This aperture is closed by the 

 peripheral end of the sense fiber. The shapes of the pits in cross 

 sections, therefore, depend on the directions in which the micro- 

 tome knife passes through the pits. The most common shape 

 of a pit in cross section is that of an urn (Fig. 9, P). Pits includ- 

 ing the pore apertures may be likened to round funnels, or to 

 funnels slightly flattened, or to funnels considerably flattened, 

 or to funnels so flattened that their tops would be club-shaped. 

 In spiders the pits are slits which pass entirely through the 

 cuticula. The sense fibers enter the pore apertures at the bot- 

 toms of the slits. The pits or slits in spiders, therefore, may be 

 likened to funnels considerably flattened. When just emerged 

 into the imago stage the pits (Fig. 9, P) in the legs generally 

 extend about one-third the distance through the chitin, but 

 when the chitin is fully developed, the pits extend perhaps from 

 one fifth to one eighth the distance through the chitin. In all 

 the figures showing two shades in the chitin, the darker one 

 (Fig. 17, Chi) represents the chitin formed at the time when the 



