APPENDIX VIII. 



THE PROGRESS OF DEVELOPMENT OF A SALMO 

 (COREGONUS PAL&A, Cuv.) EGG.* 



"\ T 7E shall try to give here a short summary of the state 

 of the embryo at all periods of its life, indicating at 

 which period the organs begin to form, and under what 

 form they first appear. 



At the time of spawning, the egg is composed of the 

 yolk, of little drops of oil spread over the surface of the 

 yolk, and forming a kind of disk ; of the germinal vesicle 

 and spots, situated in the middle of this disk ; and, lastly, 

 of the yolk and shell membranes which envelop the egg, 

 without any intermediate space between them. Four hours 

 after the spawning the shell membrane is detached from 

 the yolk membrane, in consequence of the endosmotic 

 penetration of the water through the pores of the first ; it 

 becomes inflated, and the yolk floats freely in its cavity. 

 Twelve hours after the spawning the germ begins to rise 

 from the middle of the oily disk under the form of a little 

 circular swelling. Sixteen hours after spawning the germ 

 is seen in the form of a clear, transparent vessel above the 

 oleaginous disk. The cells of which it is composed are 

 little delicate transparent vessels, without any traces of a 

 nucleus. Twenty hours after spawning the germ occupies 

 all the extent of the disk, and the furrowing begins. A 

 large shallow furrow is first perceived, which extends in a 

 circular direction, and affects nothing but the germ. Dur- 



* Translated from the French of Vogt's Embryologie dcs Sal- 

 mones, Chap. XIV., by F. W. WEBBER. 



