138 DOMESTICATED TROUT. 



At the end of a few hours, more or less, according to 

 the temperature of the water, the germ of the egg rises 

 to the top in both the fertilized and the unfertilized 

 egg, which look exactly alike. The germ in the un- 

 fertilized egg, however, undergoes no change whatever 

 from this time, while in the fertilized egg a process soon 

 begins which is called by the French embryologists 

 " sillonnement" or furrowing, and by English writers 

 " segmentation." This process begins by the sinking 

 of a deep furrow through the centre of the germ, divid- 

 ing it into two equal parts. This is followed by an- 

 other, bisecting the first, and another and another, until 

 the subdivisions have been continued indefinitely, when 

 the germ again presents nearly the same appearance 

 as at first. While this " sillonnement" or segmenta- 

 tion, is going on, the original disk formed by the germ 

 in the impregnated egg disappears, and cannot be 

 seen at all, thus distinguishing it plainly from the un- 

 impregnated egg, which still presents the germ disk as 

 clearly as ever. Therefore at this period the unim- 

 pregnated eggs can be told from the impregnated 

 ones by the one presenting the distinct germ disk, 

 while the other shows no trace of it. 



The percentage of impregnated eggs can now be 

 told approximately ; but as the light must be favorable 

 in order to tell which eggs have the germ disk visible 

 and which have not, and as it is not a good plan to 

 handle the eggs too much at this stage, it is perhaps 

 quite as well to be patient and wait till the tissues of 

 the fish are firm enough to allow the egg to be han- 

 dled, and the clearly marked eye-spots leave no doubt 



