CHANGES IN THE OVARY 129 



first polar body is discharged (after certain preparatory changes) one 

 hour after fertilisation by a spermatozoon, and that the second polar 

 body is extruded fifteen or twenty minutes later. In other animals 

 {e.g. Amphiooms), one maturation process takes place before, the other 

 during the entrance of the spermatozoon.^ 



It would appear from these facts that the maturation processes 

 in many animals only take place as a result of a specific stimulus 

 which may be induced by the act of copulation, or may be caused 

 only by the entry of the spermatozoon into the protoplasm of the 

 ovum. It would seem, on the other hand, that in some animals 

 maturation takes place independently of any stimulus at such time 

 as the follicle has attained to a sufficient degree of ripeness or after 

 it has discharged its ovum.^ 



It has already been shown incidentally that the processes of 

 maturation and ovulation are intimately associated, and that the 

 latter, like the former, is in many animals dependent for its 

 occurrence upon a definite physiological stimulus. The Graafian 

 follicle may rupture when tlie egg has reached a certain degree of 

 maturity, or it may require the additional stimulus of sexual inter- 

 course before ovulation can be induced. 



In therabbit ovulation takes place about teji hours after coition.^ 

 The ovum, which is entirely free from follicular epithelial cells, is 

 discharged into the infundibulum which at this time closely invests 

 the ovary. The discharged ovum is incapable of assimilating 

 nutriment unless it becomes fertilised, and if fertilisation is not • 

 effected it undergoes degeneration. Heape found that ovulation 

 could not be induced by artificial insemination, nor by any means 

 other than sexual intercourse, and moreover, that intercourse was a 

 sufficient stimulus, even when the progress of the spermatozoa from 

 the vagina into the uterus was artificially stopped, provided that 

 there was no interference with the vascular supply to the 

 ovaries. 



It is stated by Weil * that ovulation may take place independently 



' See Przibram, Emhryogeny., English Translation, Cambridge, 1908. 



2 The chemistry of the maturation process is discussed by Mathews ("A 

 Contribution to the Chemistry of Cell Division, Maturation and Fertilisation," 

 ATmr. Joitr. of Phys., vol. xviii., 1907). This author describes the maturation 

 of the egg of Asterias as being inaugurated by the dissolution of the nuclear 

 membrane. If oxygen is withheld the mature egg soon dies. It is believed 

 that an "oxidase" escapes from the nucleus into the cytoplasm on the 

 rupture of the nucleus. The astral radiations disappear if oxygen is with- 

 drawn, but reappear if oxygen is readmitted. It is concluded that the astral 

 figures are the product of three substances : (1) centriole substance ; (2) oxidase ; 

 and (3) oxygen. 



3 Heape, loc. cit. The maturation processes also depend on coition. 



* "Weil, "Beitrage zur Kenntniss der Befruchtung und Entwickelung des 

 Kanincheneies,-' Wien. Med. Jakrhuch, 1873. 



