324 Reciter ches sur les Poissons Fossiles. 



in drawings of fishes are the colours of death. The other 

 tints change in different ways : the red passes frequently to 

 yellow, the yellow becomes black, &c. When left in water 

 after their death, fishes become quite discoloured, yet not- 

 withstanding, if after the lapse of some time they are brought 

 into the air, their natural colour though somewhat faded, re- 

 turns.* These phenomena of coloration are so much more 

 remarkable, as in certain cases the coloured pigments appear 

 to be very fixed : particularly as they have been found in 

 fossil fishes, in which very distinct traces of the distribution 

 of their colours are preserved in the black pigment, as for ex- 

 ample, in the Platax vespertilio, Agass. the Enchelyopus 

 tigrinus, Agass. found at Mount Bolca. It is this fact 

 which induced me to speak here of the coloration of fishes. 

 I shall afterwards detail all the observations I have made 

 on this interesting subject. 



The surface of the body of living fishes is constantly 

 covered with a great quantity of mucous. With some it is 

 little tenaceous, and forms a thinish layer ; with others, and 

 particularly with those in which scales are less developed, it 

 is more firm, and forms a thicker coat, for example in the 

 Tench. The fluid is secreted by a mucous gland which ex- 

 tends the whole length of the body, and which is ramified 

 in all the bones of the head ; it is conveyed to the surface by 

 numerous pores, which are seen on the cranium and on the 

 bones of the face, on the length of the superior maxillary, on 

 the preopercule, and by a series of tubes which traverse the 

 scales of the lateral line. From these the mucous is spread 

 over the entire surface of the body, as we have proved by 

 drying the surface of fishes with a cloth; after this operation 

 they lubricate themselves anew with mucous, which flows 

 from the pores on all parts of the body. 



* In spirits of wine, fishes ratain their colours much better if previously replac- 

 ed again for a short time in water, then quickly dried in the air after having been 

 wiped. 



