Recherches sur les Poissons Foss'des. 



333 



its inferior surface or its base, it extends in its growth. 

 We have confirmed these observations by comparisons be- 

 tween a great number of different examples of scales of 

 all ages of one and the same species of fish. They will 

 form in this way a series presenting all degrees of develop- 

 ment of the scales, that we are able to observe in one 

 individual during all the periods of its growth. We learn 

 also from this, that the number of leaves which compose a 

 scale, do not correspond with the age of the fish, and that 

 in different species it is formed of a different number of 

 laminaa of growth during a year ; we find also, that the 

 growth of scales is periodical ; that they are not form- 

 ed continually without interruption, but that there are, 

 according to the species, different seasons of the year 

 more favourable to their development, during which they 

 form all the leaflets they present for the increase of 

 the year. After the consolidation of the new leaves, they 

 remain a long time, during which they are not disposed to 

 form new laminae ; the last lamina shortening itself tends 

 more or less to the border, and forms a species of hook, 

 very inconspicuous it is true, but which becomes more pro- 

 minent when the leaves of new growth are joined to it the 

 following year ; and they are then seen at the surface of all 

 the scales, as so many concentric zones, more marked in 

 proportion to the years the fish has lived. As these zones 

 are found equally visible on the scales of fossil fishes, it 

 will, in time, become the means of determining frequently 

 the age which has been attained by fossil species. 



It would be a great advantage to geology, if all the infor- 

 mation that collections of fossils are calculated to afford, 

 could be had relative to the respective ages attained by the 

 ancient beings whose remains are found in the crust of the 

 earth. If we were at first to study zealously the relations 

 which exist between the leaves of growth in the shell of 

 the mollusc as compared with the age of the animal, and 



