48 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 82 



the femur. A few pores were always found at the proximal end of 

 each tibia {e and /), and sometimes pores were found in the tibial 

 spines (G) and on the tarsi. 



In regard to water beetles, the better the legs are adapted for loco- 

 motion in water, the fewer pores they have. The smallest winged 

 species examined had 273 pores, which is the smallest number counted 

 of all the species, and the largest species had 1,268 pores which is the 

 largest number of all the species examined. The wingless species had 

 more pores on the legs than usual. As a rule, the smaller the species, 

 the fewer its pores and the larger they are, comparatively speaking. 

 As a rule, no generic and specific differences were foimd, except vari- 

 ations in number of pores, the amount of variation depending on the 

 sizes of the individuals compared. There were no individual and 

 sexual differences other than slight variations in number of pores. 



The pore apertures or pits are round, oblong, slitlike, or club- 

 shaped. On the elytra and wings (fig. 10, A and B, Ap) they are al- 

 ways round or oblong. On the legs (C) they have all four of the 

 enumerated shapes. 



The spindle-shaped sense cells (fig. 10, C, SC) of most beetles lie 

 in the lumens of the appendages outside the pore cavities. A small 

 chitinous cone (Co) is always present. It is formed by the hypoder- 

 mal cell at the mouth of the pore after the insect has emerged from 

 the last pupal instar, and at the same time when the chitinous integu- 

 ment is being considerably thickened. The sense cells are fully devel- 

 oped when the insect emerges into the imago. The sense fiber pierces 

 the cone, and comes in direct contact with the outside air. This state- 

 ment is denied by other writers. In the legs of the lady-beetle Epi- 

 lachna borealis the pore apertures lie in the center of domes (fig. 

 10, C) above the general surface of the legs. 



A large nerve and a large trachea run into each elytron (fig. 10, 

 A, A^ and Tr) and wing. In the peduncle of the elytron they run 

 through the radial plate just beneath the group of olfactory pores. 

 Branches from the nerve are given off which connect with the sense 

 cells. The large nerve and trachea passing into the wing soon divide 

 so that a smaller nerve and a smaller trachea (B, N and Tr) run 

 through each main vein. The largest trachea passes through the sub- 

 costa, and the largest nerves pass through the veins bearing the ol- 

 factory pores. These nerves give off branches which connect with 

 the sense cells. The sense cells (C, SC), wherever found, are always 

 surrounded by blood (Bl). 



In a study of the sense organs of the cotton boll weevil, the writer 

 (46) found the olfactory pores common to both the adult and larva ; 



