54 PROGRESSIVE POULTRY CULTURE 



cubation, in a horizontal position against the egg-hole 

 of the tester and looking down upon it as it is gently 

 revolved in the hand, the yolk is seen to float with the 

 blastoderm, always on its uppermost side. 



(By placing two or three fresh eggs under the sitting 

 hen or in the incubator on the second day and several 

 more on the third day after beginning the experiment, 

 the student may have at one time, eggs of one, two and 

 three days incubating, to examine. After comparing 

 these before the search-light of the egg-tester he^may 

 open their shells and carefully deposit their contents 

 in separate saucers or in glass bowls half filled with 

 water. The beginnings of embryonic development are 

 plainly visible. The blastoderm of the germ appears on 

 the upper side of the floating yolk and its color is seen 

 to be due to the blood which fills the fine net-work of 

 veins spreading out from the center of the embryo, 

 over the surface of the yolk. The circumference of the 

 collection of ramifying blood-vessels is bordered by a 

 vein which is named the sinus terminalis. As the net- 

 work of capillary veins enlarges from day to day this 

 terminating or bordering vein extends in a wider cir- 

 cumference, more and more distant from the embryo- 

 center. 



At the end of the fourth day the outer bordering 

 portion of the net-work having followed further around 

 the yolk shows decidedly darker than the central por- 

 tion, except for the dark spot which is the shadow of 

 the embryo itself. 



After five days of incubation are completed the em- 

 bryonic development has become very distinct and de- 

 cided. The blood-vessels have extended their meshes 

 fully half way around the yolk and their shadow gives 

 a dark appearance to the part of the egg that they oc- 

 cupy. The border of the shadow along the middle axis 

 of the egg shows darkest as the egg is held vertically 

 before the tester. 



The body of the embryo shows in the midst of the 

 shadow as a blurred image with a dark spot near one 

 end which is an eye. 



