90 EVOLUTION AND MAN S PLACE IN NATURE 



through a series of stages, a reproduction of the 

 species from which it has come. Like produces like. 

 The continuity of species is demonstrated in every 

 birth. However true it is that, in the early period of 

 embryonic development, the fertilised ova of different 

 species, pass through transformations startlingly 

 analogous, the distinguishing features of the species 

 to which each belongs, are uniformly presented when 

 the embryonic development is complete. Whatever 

 the argument for continuity, in respect of homologous 

 embryonic structure and function, there lies alongside, 

 equally clear and constant, evidence for the persist 

 ence of species. Organism continues its own history 

 all through its procedure for reproduction. 



In advance of this, we desire to see into the marvels 

 of germinal life, if it be possible under microscopic 

 observation to trace relative stages of progress, in 

 dicating how variation in the mature life may pass 

 over as an inheritance. 1 Artificial fertilisation, in 

 combination with ordinary phenomena of embryology, 

 has helped. Nevertheless, conjecture and specu 

 lation enter considerably into the whole discussion, 

 provocative of much scientific controversy. 



The new problem is this, How do the laws of 

 heredity provide, not only for continuity of species, 

 but for transmission of acquired characters, profitable 

 to the individual under its conditions of life ? While 

 the law of heredity clearly implies that like produces 

 like, how does the likeness pass beyond the charac 

 teristics of the species, so as to include detailed like 

 ness, and even a reproduction of the minuter features 

 of organic form involved in family life ? That these 



1 J. Arthur Thomson s Theory of Heredity, Trans. R.S.E., xvi. 91. 



