6g8 A MANUAL OF VETERINARY PHYSIOLOGY 



been found developed in the horn of the uterus on that side, 

 though the ovum was derived from the opposite ovary. Even 

 the ovary of one side and the uterine horn of the opposite side 

 have been removed without interfering with conception. Not- 

 withstanding, the simple direct method of Fallopian tube grasp- 

 ing the ovary appears the most reasonable explanation. In 

 the dog special provision exists for the ovum to pass in this 

 manner direct from the ovary into the Fallopian tube. As a 

 result of the rupture of the Graafian follicle, a rent is made in the 

 ovary. This wound fills with blood from the opened vessels, 

 and for some time afterwards appears as a pigmented spot. If 

 pregnancy has not supervened, it undergoes a retrogressive 

 metamorphosis and soon disappears. If, however, the ovum is 

 fecundated, the corpus luteum, as this pigmented spot is termed, 

 continues to grow, and may be observed in the ovary even near 

 f term/ 



The Corpus Luteum of the pregnant animal is very much larger 

 than that of the non-pregnant, and it appears to be conclusively 

 settled that the existence of this yellow tissue in the ovary is 

 not merely for the purpose of filling up a cavity in its structure ; 

 the yellow body is a ductless gland, which on pregnancy becomes 

 an active secreting agent, producing a substance by which the 

 ovum is anchored to the wall of the uterus, and its nourishment 

 and development assisted. This ductless gland is functional 

 until about the middle of pregnancy, when it is no longer a 

 necessary factor in the nourishment of the embryo, and conse- 

 quently degenerates. That the corpus luteum takes little or 

 no share in the production of seasonal sexual excitement appears 

 quite clear ; this is the function of the stroma of the ovary, 

 which pours an internal secretion into the blood, and so brings 

 about menstruation and oestrus. 



The Cell. — It will help to a clearer understanding of the structure 

 and development of the ovum if the features of body-cells in general 

 are looked at. 



There are two distinct classes of cell in the body. The more 

 numerous tissue cells, known as somatic or body cells, are responsible 

 for the structure of every tissue in the body, from the hardest to 

 the softest. Another and much smaller set are the germ cells, which 

 are solely concerned in the reproduction of the individual. The 

 somatic cells are enormously active during embryonic life, and 

 subsequently during the process of growth. When this is com- 

 pleted, they settle down to normal activity, which consists in 

 growth by the process of division ; by this process of multiplying 

 they are capable of repairing or replacing the worn-out cells of the 

 body. The living animal is merely a gigantic collection of cells, 

 each having an individual existence. As the cells die or are worn 

 out, their places are taken by others, and this process is occurring 

 from the moment the egg is impregnated to the death of the animal. 

 Within this minute speck of material is contained all the elements of 



