90 



Embryonic Development of Ovary and Testis of Mammals 



The two forms studied — rabbit and pig — are complementary in their 

 points of special suitability for this work. Although there are minor 

 differences in the development of the sex glands in these two forms, 

 yet the general process is essentially the same. In general the pig is 

 the more instructive form for a study of the early stages of embryonic 

 development, while the rabbit furnishes material better suited for the 

 study of the post-embryonic stages. 



The following tables indicate the stages studied, the sex of the 

 specimen and the number of series cut in each case. The stage of 

 development is indicated in the rabbit by the number of days and in 

 the pig by the length of the embryo. 

 Rabbit. 



f 13 D. 



14KD. 



16 D. 



17 D. 

 ! 18 D. 



19 D. 

 21 D. 

 23 D. 

 25 D. 

 {2& D. 



At Birth. 



Indif- 

 ferent. 

 1 



Female. Male. 



3 2 

 2 2 



4 2 



f 3D. 



8 D. 



10 D. 



13 D. .. 1 



17 D. .. 1 



24 D. 



25 D. .. 1 

 31 D. .. 1 



m -{ 37 D. .. 1 



45 D . . . 1 



50 D . . . 1 



78 D. .. 1 



85 D. .. 2 



93 D. .. 1 



100 D. .. 1 



130 D. .. 1 1 



[ 140 D . . . . . 1 



One each of the following stages of 

 adult rabbit ovaries ; 

 6-months-old virgin. 

 Old individual, 3 months since last 



pregnancy. 

 3K da.ys pregnant. 



s^2 



7 

 13 



14K 



16 



17 



During lactation. 



1st pregnancy. 



Stag-es. 

 0.6 ■ cm. 

 0.7 cm. 

 0.8 cm. 

 0.9 cm. 

 1 cm. 

 1. 1 cm. 

 1.25 cm. 

 1.33 cm. 



1.4 cm. 



1.5 cm. 



Pig Embryos 



Indif- 

 ferent. 



1 



1 



1 



1 



1 



1 



1 



1 



4 



Female. Male. 



1.6 



1.7 



1.8 



2.5 



3 



3.5 



4 



5 



5.7 



7.5 



8 



8.5 



10 



13 



13.5 



15 



18 



20 



cm. 

 cm. 

 cm. 

 cm. 

 cm. 

 cm. 

 cm. 

 cm. 

 cm. 

 cm. 

 cm. 

 cm. 

 cm. 

 cm. 

 cm. 

 cm. 

 cm. 

 cm . 

 cm. 



Note The pig embryos were meas- 

 ured from the cervical to the tail bend 

 in all stages up to 5 cm. length, when 

 the measurement was taken from the 

 base of the tail to the top of the head. 

 This change was made for practical 

 reasons of precision. The 5 cm. stage 

 would be about equivalent to the 4 cm. 

 stage. 



