100 BERTRAM G. SMITH 



In eggs taken from the lower oviduct there is found a slight 

 extension of the blastodisc and a marked increase in the intensity 

 of its differentiation, both in living and preserved material. 

 Moreover, outside the rather indefinite limits of the blastodisc 

 proper there seems to be a continuation of the same sort ot mate- 

 rial as an extremely thin whitish superficial layer extending beyond 

 the equator and well into the lower hemisphere. 



In eggs entering the uterus the blastodisc is well differentiated 

 throughout an area about 90° in diameter, while the entire remain- 

 ing surface of the egg shows a slight paleness as compared with 

 earlier stages. 



The dark spot or shallow depression at the animal pole persists, 

 though often very faintly, up to about the time of fertilization, 

 when its site is occupied by a minute but deep and sharply- 

 defined pit (see fig. 6). The change usually does not take place 

 until after the eggs have been for some time in the uterus. As 

 shown by the study of sections, the appearance of this pit usually 

 coincides with the time of formation of the second polar spindle. 



B. CAPACITY OF UTERINE EGGS FOR FERTILIZATION 



To test whether eggs newly arrived in the uterus are capable 

 of fertilization, a female was taken in which only a small portion 

 of the eggs had reached the uteri, the others being distributed 

 all along the route from ovary to uterus. The eggs from one 

 uterus — about 75 in number — were mixed with milt after the 

 usual manner in artificial fertilization. Of the entire lot, not a 

 single egg developed. 



In another female nearly all the eggs had arrived in the uteri, 

 a few remaining in the oviducts and body cavity, and none in 

 the ovaries. All the eggs from the uteri were mixed with milt; 

 about 5 per cent of them developed. 



In a third female all the eggs were in the uteri, but none of them 

 showed a distinct pit at the animal pole^ — evidence that they had 

 only recently entered the uterus. All the eggs were mixed with 

 milt; none of them developed. It should be noted that this 

 female was evidently in the first year of sexual maturity and the 



