OLFACTOEY HAIKS. 



51 



These olfactory liairs are partly round (Pontonia), 

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

 sometimes simply open (Fig. 39, a, 5), sometimes provided 

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

 hairs is often very considerable. Moreover, they them- 

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

 fine 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, 



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

 &, of a Pagurus ; c, of a Pinnotheres ; (i, of a Squilla ; e, of a Pontonia. 



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

 which also stand in 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, iln 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 

 terminating in a nervous fibril.* 



Leydig also mentions t the existence of small pits on 



* " Das Gelior-und Geruchsorgan der Spiunen," Arch, filr Mic. 

 Anat., 1885. 



t "Ueber Geruchs uud Gehororgauc der Krebse imd Insekten," 

 Muller's Arch., 1860. 



