OLFACTORY HAIES. 



51 



These olfactory hairs are partly round (Pontonia), 

 partly flat (Pagurus) ; the end is described as being 

 sometimes simply open (Fig.39,a,?)), sometimes provided 

 with a small cone (Fig. 39, c, d, e). The number of these 

 hairs is often very considerable. Moreover, they them- 

 selves sometimes bear, near the base, a number of very 

 fiae bristles (Pagurus). There can, I think, be no doubt 

 that these hairs are organs of sense, and . it is probable 

 that they are olfactory. The antenna of Callianassa 

 (Fig. 38) also bears another remarkable series of long, 



e d e 



Fig. 39. — Terminations of olfactory hairs of Crustacea, a. Of larva of a Paloemon ; 

 6, of a PaguruB ; c, of a Pinaotheree ; d. of a Squilla \ e, of a Pontonia. 



thin, movable, but stiff and hooked hairs (Fig. 38, g), 

 which also stand ia direct connection with the nerve, 

 and have probably some sense-function. 



In many cases the sense of smell is connected with 

 minute depressions in the integument. In spiders 

 Dahl has described a structure in the maxilla which he 

 believes to be olfactory. The skin presents a number 

 of minute orifices, under which lie elongated cells, each 

 tei-minating in a nervous fibril.* 



Leydig also mentions t the existence of small pits on 



* " Das Gehor-und Geruchsorgan cler Spinnen," Arch. }wr Mic. 

 Anal., 1885. 



t "Ueber Geruchs und Gehororgaue der Krebse und Insekten,'' 

 Miiller's Arch., 1860. 



