Structure of the Scales of Fishes. 285 



augmentations which take place in the periphery, around the cellular 

 lines ; bj' means of such augmentations, they form not only many cellu- 

 lar lines, but these longitudinal canals become themselves elongated. I 

 is very probable, that the cellular lines are formed not only one after ano- 

 ther, but that many lines are produced simultaneously. We find a proof 

 of this in the scales which preserve the marginal spaces during their suc- 

 cessive augmentations, and whose cellular lines, or the cells, are thus se- 

 parated into many groups. Of this the scales of Cobitis fossilis afford an 

 example. 



But this increase in the periphery will not explain the great thickness 

 of the centre ; we will find the cause of this in the formation of the infe- 

 rior layer. We have seen that the latter is composed of numerous la- 

 mellae ; at each augmentation new lamella? are always formed. The lon- 

 gitudinal canals which traverse the whole scale, convey the juices neces- 

 sary to produce a uniform formation of a new lamella throughout the 

 whole extent of the scale ; it follows, that the old lamellae, being sfliall- 

 est, the thickness must augment in proportion as we approach the focus. 



The development of the teeth is likewise in accordance with this opi- 

 nion. We have seen, in fact, that they are less perfect near the focus, 

 that is to say, at the place where the longitudinal canals terminate ; and 

 that they are more developed the nearer they are to the margin. Deve- 

 lojjment cannot take place without nutrition. That must, therefore, be 

 progressive, from the focus to the margin : that is to say, the less deve- 

 loped teeth on the young scale acquire development on advancing to- 

 wards the terminal edge. At the same time, new germs are forming be- 

 hind them near the focus. It would not be difficult to recognise here a 

 connection between this development and the longitudinal canals found 

 in the part of the scale which is in relation with the skin. 



The basal field is, in fact, almost entirely surrounded by the skin ; we 

 believe that we have even seen, on many occasions, the filaments which 

 enter into the longitudinal canals. We see, then, after what has been 

 said, what an intimate relation these canals have to the development, 

 and that they perform, so to speak, the function of roots to the scale, 

 t Perhaps an observation now to be noticed, may be regarded as still 

 further corroborating this opinion. The scales of many species of the genus 

 Abramia have appeared to us to lose their longitudinal canals at an ad- 

 vanced age ; for we have seen some of them on other individuals which 

 presented no difference but in size. These canals would then become 

 filled, and, as it were, obliterated hy age, a phenomenon by no means 

 singular in anatomy. 



Do these canals, it may be asked, themselves convey the juices, or are 

 they only tubes for the lymphatic vessels ? Future researches must de- 

 cide this question, Fr the present, we consider it enough to have de- 

 monstrated the relations which subsist between the growth of the scale 

 and these canals, and the important part which the latter perform in the 

 anatomy and physiology of the scale. 



VOL. XXVIII. NO. LVI. APRII- 1840. W 



