OLFACTORY ORGANS OF A COLEOPTEROUS LARVA 129 



The writer did not spend any time studying the innervation of 

 the hairs under discussion, for vom Rath ('88) has already deter- 

 mined that each bunch of hairs is provided with a sense cell group, 

 from which runs a sense fiber to the base of each hair. 



SUMMARY 



So far as known to the writer, the two types of olfactory organs 

 herein discussed are reported for the first time in a larva. The 

 single olfactory organs have been seen by various observers, but 

 have never been identified as the organs, called the olfactory 

 pores by the writer. The compound olfactory organs have 

 certainly been observed, but hkve probably been regarded as the 

 pore-plate sense organs, so common to the antennae of adult 

 insects. 



In regard to structure, the olfactory pores are like those in 

 adult beetles, with the exceptions that their pore apertures do 

 not communicate externally with pits and that the borders sur- 

 rounding the pore walls are striated. The compound organs are 

 patterned after the single organs, but since the available space 

 inside the tip of an antenna is limited and as the integument must 

 not be materially weakened, the following two modifications are 

 present; 1) the sense cells lie in closely compact groups, thereby 

 causing a long and very slender form, whereas those belonging to 

 the single olfactory organs are shorter and much larger in diam- 

 eter; and 2) many pore apertures lie in the same plate, more 

 closely together than would be possible for the pore apertures 

 belonging to single organs. By this means the least possible 

 amount of the integument is devoted to pore cavities, thereby 

 weakening the integument as little as possible, and at the same 

 time rendering a larger number of pore apertures possible. 



The single organs are more widely distributed in the larvae 

 than in the adult beetles; in the former they are found on the 

 head, on all of the head appendages, legs and hypopleural regions ; 

 and in the latter on the elytra, wings and legs, and probably 

 elsewhere, although they have never been looked for on other 

 parts of the integument, but it is unlikely that they will ever be 

 found on the antennae and thorax. 



JOURNAL or MORPHOLOGY, VOL. 31, NO. 1 



