Incubation 



1S59 



help to make the person testing the eggs more expert, and will add 

 interest to the work. 



An infertile egg that is being tested has the same appearance as a fresh 

 egg, the only apparent difference being in the size of the air cell. In Fig. 70 

 may be seen several types of eggs and conditions of development as they 

 appear after seven days of incubation. Dead germs are found on the 

 seventh day in various forms and sizes, the most common of which are 

 shown in Fig. 71 (2, 3, 4, 5, and 6). All these types should be discarded. 

 Blood rings, also shown in Fig. 7 1 , are caused by the bursting of the blood 

 vessels, due to overheating or to other reasons causing a weakened condi- 

 tion of the embryos. 



Fig. 69. — ^1 convenient arrangement for sunlight testing: i, Tray for untested eggs; 2, 

 tray for good eggs; j and 4, trays for infertile and dead germ eggs; ^, curtain -in place 



The second test is more difficult to make than is the first. Many of the 

 weaker germs will not differ materially in appearance from those that are 

 dead, and some that have died within a few days of the time of the test 

 cannot be distinguished from the living embryos. However, if an egg 

 contains a strong living germ, the germ will be dark in color and apparently 

 fairly well developed ; the space below the membrane forming the air cell 

 will be filled, making the division dark and firm; and occasionally life will 

 be denoted by motion within the egg. The less developed the embryo 

 appears to be, the fewer are the chances of its hatching. If the egg con- 

 tents immediately below the air cell appear uneven and indistinct, and if 

 the remainder of this division shows no development of the embr^^o as in 

 the other eggs, it may be concluded that the germ is dead. 



