INTRODUCTION. 69 



part near the eyes there are above thirty small 

 ducts sent off, which open on the surface of the 

 skin. But besides this very picturesque duct, 

 there is on each side of the fish, a little farther 

 forwards than the foremost of the five breathing 

 holes, a central part from which a prodigious 

 number of ducts issue, to terminate on almost 

 the whole surface of the skin, excepting only the 

 snout or upper jaw. At these centres the ducts 

 are all shut, and in their course have no commu- 

 nication with each other.* In the skate the whole 

 cellular substance of the nose or snout secretes 

 a mucus, which is dispersed by bundles of tubes 

 opening exteriorly. The Eel and Couger have large 

 openings at different parts of the nose, communi- 

 cating with numerous lengthened vessels analo- 

 gous to the winding canals of the Skate.f But in 

 almost every fish these have a distribution diffe- 

 rently managed according to their wants, forming 

 one of the most beautiful and necessary provisions 

 in their whole structure. That of the Cod. from 

 its simplicity, will best shew it, reduced from one 

 of the characteristic plates of Monro. 



* Monro, pi. ri. viL t Cuvier, i. 252. 



