THE OLFACTORY SENSE OF COLEOPTERA. 425 



Neu) of the nerve is usually distinct. In the cross section of a 

 nerve, the nervous substance appears more or less netlike and 

 nuclei, probably neuroglia nuclei (Fig. 17, NeurNuc), stand out 

 conspicuously in the network. The trachea (Figs. 16, 17 and 

 28, Tr) and nerves (N and NB) are firmly suspended by the 

 connective tissue whose nuclei {ConTNuc) are seen only occa- 

 sionally. The lumen of the leg at the proximal end of the tibia 

 of Epilachna seems to be divided into two chambers by a mem- 

 brane (Fig. 17, Hypi) which resembles hypodermis. This 

 structure has never been seen before by the writer and nothing 

 can be said about its function. 



The hypodermis (Fig. 18, Hyp) beneath the olfactory pores in 

 the peduncles of the elytra is much thicker than elsewhere. It 

 usually contains all the sense cells (SC), but in the elytra of 

 Passalus the hypodermis is thinner and since the sense cells are 

 so large and so numerous there is not enough room for all of 

 them in the hypodermis. For this reason only a few of them 

 lie among the hypodermal cells and the remainder of them lie 

 in the lumen of the peduncle between the hypodermis and nerve. 

 As usual they are surrounded by blood. In only one instance 

 was the writer able to trace a sense cell all the way from the 

 pore aperture to the nerve. Fig. 23 represents this sense cell 

 connecting with the pore aperture (PorAp) and with the nerve 

 (N). The trachea (Tr) lies by the side of the nerve. A large 

 nerve (Fig. 29, N) and a large trachea (Tr) run through the 

 radial plate (RP) of the peduncles beneath the olfactory pores. 

 From the nerve many branches are given off which connect with 

 the sense cells. 



The hypodermis (Fig. 22, Hyp) beneath the olfactory pores 

 in the wings is usually much thicker than elsewhere, but it does 

 not contain the sense cells (SC). These cells lie in a blood sinus 

 (Fig. 22, BlSin) between the hypodermis {Hyp) and the trachea 

 {Tr), nerve {N) and nerve branches {NB). In the wings it is 

 usually difficult to trace a sense fiber all the way to the pore 

 aperture, but in oblique superficial sections this is easily done 

 (Fig. 30). A large nerve and a large trachea run into each wing. 

 These divide so that a smaller nerve and a smaller trachea run 

 through each main vein. The largest trachea (Fig. 31, Tr) runs 



