i;288 M. Agassiz on Dr Mandra Observations on the 



tions made by him on the structure of the scales of fishes, and 

 that his conclusions differed from those which I had published 

 on the same subject. Not being, however, precisely aware 

 of the nature of his objections, I had necessarily to delay mak- 

 ing a reply till his memoir was published. Since it appeared 

 in the Annales des Sciences Naturelles, in October last,* I have 

 carefully revised all the observations I published about ten 

 years ago, on the genera and species of fishes brought from 

 Brazil by Spix, and wliich I had described during my resi- 

 dence at Munich in 1829. I have also repeated my observa- 

 tions on the scales of fishes in general, the results of which I 

 had stated in one of the introductory chapters of my Sesearches 

 on Fossil Fishes. By mentioning these facts, I wish to con- 

 vince the Academy that it is not by trusting to old recollec- 

 tions that I engage to refute the very trivial assertions of M. 

 Mandl, but after a fresh examination of the whole question. 

 It is of importance to me in other respects that I should in- 

 sist on this point, and make the case known as it really stands, 

 for M. Mandl so often repeats in his memoir, that the diffe- 

 rences between his obsei'vations and my own, result from the 

 inadequate means of observation at my disposal, that it might 

 be supposed he was quite familiar with everything that goes 

 on in my study, instead of being, as he is, an entire stranger 

 to me. M. Mandl, however, who piques himself on being so 

 perfectly at home in every thing relating to microscopical in- 

 vestigation, both in France and in other countries, ought to 

 be made aware that I possess an excellent microscope by 

 Frauenhofer, of a peculiar construction, of which a description 

 with plates, was published in 1830 by M. Dollinger, the illustri- 

 ous physiologist of Munich, who has thrown so much light, by 

 his microscopical researches, on embryology and the circulation 

 of the blood in the. capillary vessels. The instrument in ques- 

 tion was regarded by this individual as the best then knovra. 



I shall state further, that the observations, the result of 

 which I am about to announce, were made on the scales of up- 

 wards of 300 species, belonging to all the families of the class 

 of fishes, without taking into account the numerous observa- 



* MancU's observations will be found at pp. 113 to 12C, and pp. 274—287. 

 of this volume of the Plii], Jouma], 



