134 THE PHYSIOLOGY OF REPKODUCTION 



phenomena depends upon the act of fertilisation. For example, 

 in the Japanese Palolo-worm, a marine Polychaet Annelid, 

 Izuka l has shown that the 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. 

 Amphioxus), one maturation process takes place before, the 

 other during the entrance of the spermatozoon. 2 



It would appear from these facts that the maturation pro- 

 cesses 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 proto- 

 plasm 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. 3 



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 the egg has reached a certain 

 degree of maturity, or it may require the additional stimulus of 

 sexual intercourse before ovulation can be induced. 



In the rabbit ovulation takes place about ten hours after 

 coition. 4 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, 



1 Izuka, "Observations on the Japanese Palolo," Jour, of the Coll. of 

 Science, University of Tokyo, vol. xvii., 1903. 



2 See Przibram, Embryogeny, English Translation, Cambridge, 1908. 



3 The chemistry of the maturation process is discussed by Mathews 

 (" A Contribution to the Chemistry of Cell Division, Maturation and Fertilisa- 

 tion," Amer. Jour, 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 

 withdrawn, 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. 



4 Heape, loc. cit. 



