366 ALBERT C. EYCLESHYMER. 



directly to a lack of sufficient oxygen, the incubator in which 

 the experiments were made being poorly ventilated, owing to the 

 fact that the ventilating system had been modified in order to 

 compare its results with those provided with special ventilation. 

 A second incubator provided with a special ventilating apparatus, 

 hatched 83 per cent, and 88.6 per cent, of two lots of eggs taken 

 from the same fowls. 



Dareste concluded from his experiments that during the first 

 week of artificial incubation, eggs which are unturned develop in 

 essentially the same manner as those which are turned. The 

 principal cause of death is due to the allantois growing fast to the 

 yolk, causing the rupture of the vitelline membrane, thereby 

 allowing the yolk to escape so that it cannot be taken into the 

 body of the embryo. Dareste adds that when the eggs are 

 turned it is probable that the position of the allantois is shifted, 

 and this movement prevents its adhesion to the yolk. It should 

 be remarked that during the early days of incubation it is also 

 necessary to turn the eggs frequently ; otherwise, the embryo 

 grows fast to the shell membrane: This has not only been 

 shown by the preceding experiments, but has been repeatedly 

 observed in other eggs. 



IV. TEMPERATURE OF EGGS'. 



Repeated attempts have been made to ascertain the tempera- 

 ture of the egg during natural incubation, but as yet the 

 results are far from satisfactory. This is due to the difficulty 

 experienced in testing the temperature of different parts of the 

 egg. The fact that the egg comes in contact with a heating sur- 

 face above and a cooling surface below, leads to most perplexing 

 complications. While the temperature of the hen is easily ascer- 

 tained, it is not an easy matter to know the precise degree of 

 heat applied to the surface of the egg. Moreover, it should be 

 kept in mind that during incubation, not all the eggs are at all 

 times in contact with the body of the hen. A layer of feathers 

 intervenes to modify the temperature, this layer varying greatly 

 in thickness in different parts of the body, and at different times 

 during incubation. All these factors conspire to make an 

 exceedingly difficult problem. 



