GUSTATORY AND OLFACTORY TISSUES 265 



pits have this inner wall arising from a higher or more distal height and 

 everted into a long, sharp, curved hair instead of the round, club-shaped 

 organ seen in the deeper pit. The proximal layer is of a different kind 

 of chitin and stains a different shade altogether, with most stains. It is 

 not a layer in the proper sense of the word, being a set of proximal pro- 

 jections from the real chitin layer. 



The nerve cells are readily recognized among the hypodermal cells 

 by their thicker body and larger, clearer, and rounder nucleus. They lie 

 with their main cell body in the proximal third of the layer, and thus their 

 nuclei are found among those of the hypodermis cells. The cell body is 

 drawn out distally and enters into one of the pit knobs or hairs. Both 

 kinds are sensory, and knowing what we do about the tactile hairs of 

 insects, it is fair to believe that the hair-covered endings are tactile, while 

 the knob-covered endings are olfactory. 



The knob-covered endings which rest in the deep pits are entirely 

 homologous with the hairs. They are but shorter, blunter, and more 

 deeply set hairs. They also exactly represent the " pegs " and other 

 olfactory processes of Hauser, Graber, and many other writers. The 

 nerve-cell cytoplasm which they contain is granular and represents a 

 special cell organ of olfactory perception. It is aways protected from 

 the exterior by the cuticle, and in no case were the writers able to find a 

 case where the cytoplasm of either an olfactory pit, peg, knob or hair 

 organ had direct access to the air. At first the broken and cut hair 

 endings give this impression, but it soon becomes easy to detect the arti- 

 fact. 



The proximal end of the cell is drawn out into a nerve fiber, which 

 runs in to connect with some ganglionic center. In connection with 

 this nerve fiber one often sees a peculiar black line (in iron haematoxylin- 

 stained specimens) which enters the epithelium and passes directly 

 through it to the cuticle. Following this line back out of the epithe- 

 lium, it is seen to reach one of the large cells mentioned above and enter 

 into a vacuole-like area of this cell, where it ends in a cylindrical enlarge- 

 ment of some little length. These cells are large, with nuclei that are 

 round and full and a cytoplasm that is granular, as in a nerve cell. At 

 first sight they are liable to be taken for nerve cells, but must probably 

 be considered as gland cells, and the line for a cuticular tube which ends 

 in their vacuolar area much as the homologous tube does in the secretory 

 cell of the odoriferous glands of Belostoma. The end cylinder is sur- 

 rounded by a thicker covering of some less dense material. The per- 

 ceptory or distal opening of the line tubule could not be made out. 

 These very peculiar organs have been thought to be associated with 

 the sense of smell, and the auditory and the static functions. They 

 are probably, as far as we can determine for the present, cells that secrete 



