82 



THE EGGS OF MAMMALS 



has observed an exactly similar initial shrinkage followed 

 by a return to normal in rabbit ova seminated in vitro. 



TABLE XII 



The Volume of Rat Eggs in Three Stages of Development. 

 Gilchrist and Pincus, 1932) 



(From 



Stage 



Follicular 

 Tubal, un- 

 fertilized 

 1-cell 



Average Volume of 

 Round Eggs, cu. mm. 



0.000333 (1) 



0.000251 

 0.000202 



0.000023 

 0.000009 



Average Volume of 

 Elongated Eggs, 



0.000339 ± 0.000017 



0.000226 

 0.000200 



0.000013 

 0.000010 



Average Volume of 

 All Eggs, cu. mm. 



0.000337 ^ 0.000010 



0.000234 

 0.000201 



0.000018 

 0.000010 



TABLE XIII 



The Size of Rat Eggs under Various Conditions of Culture. (From 

 Gilchrist and Pincus, 1932) 



Treatment 



Incubated in Ring- 

 er's solution 

 alone 



Incubated with 

 live sperm 



Incubated with 

 dead sperm 



Num- 

 ber 



OF 



Eggs 



Average 



Diameter 



Immediately 



AFTER 



Putting 

 Eggs on 



Slide, 

 Microns 



74.4 ± 1.4 

 77.9 ± 1.4 

 72.8 ± 1.1 



Average 

 Volume 

 Calcu- 

 lated, 

 cu. mm. 



0.0002 IG 

 0.000248 

 0.000204 



Average 

 Diameter 

 Some Time 



AFTER 



Incubation, 

 Microns 



76.3 ± 0.4 

 72.7 ± 1.4 

 69.7 ± 1.3 



Average 

 Volume, 



Calcu- 

 lated 



cu. mm. 



0.000232 

 0.000205 

 0.000179 



Shrink 

 age. 

 Per 

 Cent 



17 

 12 



Sperm penetration into living ova has been observed 

 only once (Pincus, 1930); a modified fertilization cone ap- 

 pears to form at the point of contact. This cone very 

 quickly subsides as is apparent also from fixed preparations 

 of mammalian ova in the tubes {e.g., Lams and Doorme, 

 1908; Sobotta and Burkhard, 1911 ; Lams, 1913; and others). 



The length of time that the mammalian ovum remains 

 capable of fertilization has been largely a matter of specu- 

 lation. Exact experimental inquiry has, however, been 

 undertaken in the rabbit (Hammond and Marshall, 1925; 

 Hammond, 1928 and 1934) and in the ferret (Hammond and 

 Walton, 1934). Taking advantage of the fact that the 



