CHAPTER XII. 



Theory of Fertilisation. 



In his 49th Exercitation on the " efficient cause of the chicken," 

 Harvey thus quaintly expresses what has ahva)'S been, and still 

 is, a baffling problem : — " Although it be a known thing sub- 

 scribed by all, that the foetus assumes its original and birth 

 from the male and female, and consequently that the egge is 

 produced by the cock and henne, and the chicken out of the 

 egge, yet neither the schools of physicians nor Aristotle's dis- 

 cerning brain have disclosed the manner how the cock and its 

 seed doth mint and coine the chicken out of the egge." The 

 old theories on the subject are more curious than profitable, a 

 fact not to be wondered at since it is really only within the 

 last fifty years that the fundamental fact of the union of the 

 sex-cells has been observed. 



§ I. Old Theories of Fertilisation. — (^7) From Pythagoras 

 and Aristotle on to the "Ovists," of whom we have already 

 spoken (p. 84 ), numerous naturalists have held the opinion 

 that the ovum was the all-important element, which only 

 required to be awakened to development by contact with the 

 male fluid or male elements. It must be allowed, that while 

 ova may exceptionally develop without sperms, the latter never 

 come to anything apart from ova. This will be less insisted on, 

 however, when it is recognised that in reality the ovum is not so 

 fiiirly comparable with the spermatozoon as with the mother- 

 sperm-cell. It must be allowed, too, that there is much to 

 warrant us in thinking of the sperm as an element which 

 stimulates the ovum to division ; yet this will be recognised as 

 only approximate language, when the facts of the intimate 

 nuclear union are fully appreciated. 



{li) In contrast to the above opinion, we find ingenious 

 thinkers, so widely separate in time as Democritus and Paracelsus, 

 regardiiig the male fluid as very important, forestalling Buff'on 

 and Darwin in fact in considering it in a sense an extract or 



