Dr John Davy on the Ova of the Salmonidce. 22 1 



forward the fundamental principle, that mineralogists should 

 only pay attention to the natural history characters of mine- 

 rals, such as crystalline form, hardness, specific gravity, and 

 not to such as cannot be observed without causing a sensible 

 alteration in the substance. If it ever happens, — continues 

 Mohs, — that a branch of natural history as mineralogy, em- 

 ploys such characters in its method as these last mentioned, 

 it then exceeds its legitimate bounds, becomes entangled with 

 other sciences, and hampered with all those difficulties of 

 which mineralogy has long been a warning example. 



(To be concluded in our next.) 



_ 



Some Observations on the Ova of the Salmonidce. By John 

 Davy, M.D., F.R.S., &c. Communicated by the Author. 



M. Vogt, in his able and elaborate work on the Embry- 

 ology of the SalmonidEe, has pointed out a remarkable pro- 

 perty belonging to the ova of these fishes, viz., that of hav- 

 ing their fluid contents coagulated by admixture with water. 

 — Thus, as he states, " Lorsqu'on creve un oeuf dans l'eau, 

 on voit a l'instant raeme la masse entiere du vitellus se trans- 

 former en une matiere blanchatre, lactee, opaque et filamen- 

 teuse, qui n'a plus aucune ressemblance avec la substance 

 vitellaire de l'oeuf intacte. Voulant m'assurer si c'etait 

 reellement l'effet de l'eau, j'ouvris un oeuf au foyer du micro- 

 scope et j'y melai une goutte d'eau, pendant que j'observais 

 le vitellus : partout ou les deux liquides entrerent en contact 

 il en resulta a l'instant meme une quantite de petite granules 

 opaques, qui furent affected pendant long temps d'un mouve- 

 ment molleculaire tres pronounce. Ces granules etaient si 

 petits que sous mon plus fort grossissement, ils ne m'apparu- 

 rent que comme de petits points fonces et leur nombre con- 

 siderable me prouva suffisament que ce n'etaient pas des 

 | nucleolules devenus libres par l'effet de l'eau qui auraient 

 fait crever les parois des cellules."* 



* Embryologie des Salmones, par C. Vogt, p. 11, in vol. i. of M. Agassiz'a 

 Hist, of Fresh- Water Fishes, Neuchatel, 1842. 



VOL. LIU. NO. CVL— OCTOBER 1852. Q 



