n8 PHYSIOLOGICAL 



or got rid of. Similarly if the ovum be not fertilized it also dies 

 and the substance of which it is formed breaks up and becomes 

 lost. The union of the ovum and the spermatozoon is the really 

 essential act in the reproductive process, the ovum becoming 

 thereby endowed with a new vitality whereby it is rendered 

 capable of undergoing those wonderful developmental processes 

 which culminate in the full formation of a completely formed 

 individual similar to those from which the ovum and spermato- 

 zoon were derived. 



But as already mentioned, the ovary, in addition to the primary 

 function of producing the female reproductive cells or eggs, 

 has the further function of controlling the oestrous or sexual 

 cycle. This it does by means of certain chemical substances 

 or internal secretions which the ovary elaborates and which are 

 passed into the circulating blood and carried to all parts of the 

 body. These internal secretions which vary in quantity and 

 in composition at the successive stages of the cycle act upon 

 the mammary glands, the uterus and other sexual organs and 

 excite or call into operation the periodic growth and activity 

 which these organs from time to time display. The ovary is 

 continually engaged in manufacturing these secretions; if the 

 animal be spayed before sexual maturity the accessory organs 

 (uterus, mammary glands, etc.) fail to develop; if the ovaries 

 be removed after maturity the uterus and other organs cease 

 to function and undergo atrophy. 



For some time prior to oestrus the ovaries show an increased 

 activity ; this is manifested partly in the growth of the vesicles 

 which contain the ova, but there is every evidence that the 

 internal secretions of the ovaries are also produced in greater 

 quantity. Thus the uterus undergoes growth, and eventually 

 passes through a period of congestion which characterizes 

 the period of "heat." During the latter part of this period 

 ovulation takes place, and then the ovary undergoes a remark- 

 able change. The vesicle from which the egg was discharged 

 instead of merely shrivelling up as one might reasonably expect 

 to happen, becomes transformed into a large yellow body which 

 is highly congested, and comes to protrude from the surface 

 of the ovary in much the same kind of way as the original follicle 



