_ 1899-1900.] Fish-Hatching at Howzetoun. 115 
box. From statistics of temperature of the water, it is 
possible to predict with accuracy the date at which any 
particular batch will hatch out. 
In fish culture there are five distinct stages. The first, or 
_ mulberry stage, occurs about the close of segmentation. The 
round disc rises in all ova during the first twenty-four hours, 
_ but during the. period of segmentation the disc in properly 
fertilised eggs becomes har and in unimpregnated eggs 
annular. At the close of the period of segmentation the tise 
in properly fertilised eggs enlarges, and has a soft appear- 
ance, so that it is easy to detect and remove all ova likely to 
develop imperfectly. Absolutely unimpregnated eggs show a 
well-defined annular ring when a third of the eer of in- 
cubation is over, and they can then easily be removed. Im- 
perfectly impregnated ova call for some care, as they do not 
show the well-marked embryotic layers. 
The second stage is known as the spectacle stage, and is 
occasioned by the appearance of a loop of globules anterior to 
the embryotic line. This loop gradually enlarges and passes 
backwards over more than half the sphere, giving the egg at 
one time the appearance of a pair of spectacles minus one eye. 
The left side of the eye of the spectacle stops in the position 
shortly to be occupied by the principal duct of the yolk-sac 
circulation, and the right side gradually disappears. From the 
ime of the appearance of this spectacle marking and the 
ate of its development, the vitality of the embryo can be 
estimated. 
The third stage is the eye stage, and at this time the tail is 
free. The si cneae of warmth causes a slight movement of 
the tail, and it is important that ova are not ipaced for export 
until this movement can be discerned. 
_ The fourth stage is marked by the appearance of red blood, 
and one-half of the period of incubation is passed. The ova 
can now stand any fair usage, and can be packed for export 
and endure a long journey. 
The fifth stage—the completion of the embryonic circle— 
immediately precedes hatching. The tail curls round generally 
to the right, and passes the nose. The body of the embryo 
thas now become dark, and the yoke globules have mostly 
collected immediately below the stomach. 
' VOL. IV, I 
