THE BEGINNINGS OF LIFE. 97 



but recently come into being 1 . After a careful sum- 

 mary of what is known on the subject, Mr. Spencer 

 says : c The assumption to which we seem driven by 

 the ensemble of the evidence is, that sperm-cells and 

 germ-cells are essentially nothing more than vehicles 

 in which are contained small groups of the physio- 

 logical units in a fit state for obeying their proclivity 

 towards the structural arrangement of the species they 



belong to Thus, the phenomena of Heredity 



are seen to assimilate with other phenomena; and 

 the assumption which these phenomena thrust on us 

 appears to be equally thrust on us by the phenomena 

 of Heredity. We must conclude that the likeness of 

 any organism to either parent is conveyed by the 

 special tendencies of the physiological units derived 

 from that parent. In the fertilized germ we have 

 two groups of physiological units, slightly different 

 in their structures. These slightly different units 

 severally multiply at the expense of the nutriment 

 supplied to the unfolding germ, each kind moulding 

 this nutriment into its own type. Throughout the pro- 

 cess of evolution the two kinds of units mainly agreeing 

 in their polarities and in the form which they tend to 

 build themselves into, but having minor differences, 

 work in unison to produce an organism of the species 



1 See vol. i. pp. 1 99-207. We have already pointed out the great evolu- 

 tional capacities that seem to be possessed by the phosphoric fats, which 

 enter so largely into the composition of ova (vol. i. p. 2 1 a). These fats are 

 Closely allied to myeline and other remarkable fatty extracts (see p. 118). 



VOL. II. H 





