PHYSIOLOGICAL n 7 



second hand, and, if there be one, the partially detached mechan- 

 ism of the striking apparatus, are dependent upon the main- 

 spring, so the sexual cycle, both the complete annual cycle and 

 recurrence of the three- weekly periods, and also, though in a 

 more remote and complex way, the recurrent changes which 

 take place in the mammary glands and the growth of the 

 uterus in pregnancy, are controlled and periodically influenced 

 by the dominating activities of the ovary. 



The primary function of the ovaries is to produce the ova or 

 eggs. These are enclosed in little bags or sacs called follicles, 

 which begin by being very small and then gradually increase 

 in size as they approach maturity, and in the last stages of 

 ripening come to protrude visibly from the surface of the organ. 

 When the cow is "on heat" or "in use" one (rarely two or 

 more) of these follicles ruptures and discharges the ripe egg 

 along with the liquid contents of the follicle into the body cavity. 

 This act, namely the rupture of the follicle and the discharge 

 of the ovum, is known as ovulation. The ova are microscopic 

 in size or only just large enough to be detected with difficulty 

 by the naked eye. Each ovum shed from the ovary in the way 

 described is normally caught up in the trumpet-shaped end 

 of the oviduct, which is a fine, somewhat coiled tube leading 

 on each side of the body cavity from a position close to the 

 ovary to the corresponding horn of the uterus or womb. The 

 two horns of the uterus unite together further back to form 

 the body of the uterus; the latter communicates posteriorly 

 through a narrowed neck with the much larger passage, the 

 vagina, through which the calf is carried in the act of parturition, 

 and through a portion of which the urine also passes after being 

 evacuated by the bladder. 



After ovulation, which as we have seen takes place when the 

 cow is "on heat" (i.e. during oestrus), the ripe egg passes down 

 the oviduct. If the cow has been served the uterus and oviduct 

 will as a rule contain very numerous spermatozoa or reproduc- 

 tive cells coming from the testicles of the male ; nevertheless in 

 the fertilization of one ovum only one spermatozoon participates, 

 the rest of the spermatozoa dying in the female passages, their 

 cell substance becoming disintegrated and eventually absorbed 



