208 THE BEGINNINGS OF LIFE. 



the rule for the germinal vesicle to disappear. Dr. 

 Allen Thomson says: c ln some animals, as Mam- 

 malia and Birds, it has been observed that shortly be- 

 fore the diffluence of the vesicle its delicate wall under- 

 goes a softening on approaching solution, so as to make 

 it impossible to separate the vesicle entire. After this, 

 when the diffluence is complete, the contents disappear 

 from the situation they have previously occupied, but 

 what becomes of them has not yet been determined.' 

 Thus, at all events, we get rid of the only element of 

 the ovum about whose precise mode of origin there is 

 any doubt or uncertainty. We are now reduced to a 

 mere amorphous mass of granular material dispersed 

 through a homogeneous basement substance. But in 

 the midst of this mass there shortly arises de novo, in 



The fecundating power of the semen is an expression used only for 

 convenience to denote the invariable sequence or relation as cause 

 and effect which has been observed to subsist between the contact of 

 spermatic matter with the ovum, and the. changes in the latter which 

 follow on the act of fecundation. We might with as much propriety 

 have given a name to a separate power residing in the egg or its germ, 

 which render it susceptible of fecundation, as of a special power belong- 

 ing to the semen by which that susceptibility of the ovum is acted upon. 

 The efficient cause of the process of fecundation can only be educed, as 

 in all physical as well as vital changes, from a perfect knowledge of all 

 its phenomena, and the statement of the efficient cause of such actions 

 is only the expression of the most general and best known law to which 

 a full acquaintance with the phenomena enables them to be reduced. 

 Fecundation is to be regarded as a purely vital change, seeing that it 

 takes place only in the usual conditions of vitality ; but, like all other 

 vital changes, it appears more probable that a variety of conditions of 

 the organic matter, rather than any one known property or condition, 

 are necessary for its occurrence.' (Loc. cit. p. 138.) 



