no 



FISHES. 



Fio 



47. — Nostrils of Raia Umprieri, with 

 nasal flaps reverted. 



movith. The pituitary membrane is transversely folded, the 



transverse folds being di- 

 vided by one longitudinal 

 fold. The walls of the sac 

 are strengthened by sun- 

 dry small cartilages. 



Also in Chondroptery- 

 gians the openings, of 

 which there is one to 

 each sac, are on the lower 

 part of tlie snout, and in 

 the Eays,Holocephali, and 

 some Sharks, each ex- 

 tends into the cleft of the 

 mouth. The openings are 

 protected by valvular flaps, supported by small cartilages, 

 and moved by muscles, whence it may be concluded that 

 these fishes are able to scent (actively) as well as to smell 

 (passively). 



In the majority of Teleostei the olfactory capsules are 

 lateral or superior on the snout, covered externally by the 

 skin, each usually pierced by two openings, which are either 

 close together, or more or less remote from each other ; the 

 posterior is generally open, the anterior provided with a valve 

 or tube. In the Chromides and Labroidei ctenoidei a smgle 

 opening only exists for each sac. In the Murwnidce the two 

 openings of each side are either superior, or lateral, or labial, 

 that is, they are continued downwards and pierce the margin 

 of the upper lip. In many Tetrodonts nasal openings are 

 absent, and replaced by a conical papilla, in which the olfactory 

 nerve terminates. 



It is certain that fishes possess the faculty of perceiving 

 odours, and that various scents attract or repel them. A 

 mangled carcase or fresh blood attracts Sharks as well as the 



