BREEDING. 29 



inch; at twenty-four days, 1-2 to 3-5 inch. The umbilical vesicle 

 has reached its maximum size. At twenty-eight days the embryo 

 has a leng'th of 1 inch; at thirty-seven days, 2 1-5 inches. 

 Length of embryo in the eighth week is 3 1-5 inches. At the 

 ninth and tenth month it measures 5 1-5 inches. At the fifteenth 

 it measures about 7 inches in length. At the sixteenth or seven- 

 teenth week the fetus has a length of 10 inches. 



Caka'ivora. — The dog's embryo measures about one line in 

 length at the second week. The chorion and amnion can be made 

 out. At the third week the villi appears on the chorion, and 

 becomes attached to the mucous membrane of the uterus. At 

 eighteen days the embryo of the dog has a length of about 1-5 

 inch; the primitive groove and chorda dorsalis are present. At 

 nineteen or twenty days the heart is present as an S-shaped tube; 

 the intestine begins to form. At twenty-one days indications of 

 the eyes, ears, and Wolffian body are present; the limbe are 

 present as small blunt processes. At twenty-two to twenty-three 

 days the embryo has a length of about 3-5 inch; mouth groove, 

 nostrils, lungs, trachea, and larynx are present; the anus is still 

 closed; Wolffian body well formed; limbs about one line in 

 length. At twenty-five days the thorax is closed, and the abdom- 

 inal cavity almost closed. At twenty-six to twenty-eight days 

 the embryo is about 1 3-5 inches in length; all organs are more 

 or less distinctly marked. Length of embryo in the fifth week 

 is 2 3-5 inches; at six weeks, 3 1-5 inches. At eight weeks the 

 dog's embryo measures 5 inches; the cat's embryo, 4 inches. 

 The body is covered with hair, and the claws are present. The 

 eyelids are closed, and the testicles are still in the abdomen. At 

 nine weeks the dog's fetus measures about 7 inches; the cat's 

 fetus about 5 inches. 



PARTURITION. 



When the fetus is expelled from its uterine cavity, before the 

 period of viability, the process is termed abortion or miscarriage. 

 When the expulsion occurs during seventh or eighth month it 

 is tenned premature labor. Why the uterus expels its contents 



