IN THE LAST HALF- CENTURY. 117 



mentally the same. Moreover, the higher 

 forms are evolved from lower, in the 

 course of their development, by analogous 

 processes of differentiation, coalescence, 

 and reduction in both the vegetable and 

 the animal worlds. 



At the present time, the cell theory, in 

 consequence of recent investigations into 

 the structure and metamorphosis of the 

 'nucleus,' is undergoing a new develop- 

 ment of great significance, which, among 

 other things, foreshadows the possibility 

 of the establishment of a physical theory 

 of heredity, on a safer foundation than 

 those which Buffon and Darwin have de- 

 vised. 



The popular belief in abiogenesis, or Sponta- 

 the so-called ' spontaneous ' generation of genera- 



. tion dis- 



the lower forms of life, which was ac- proved, 

 cepted by all the philosophers of antiqui- 

 tv, held its ground down to the middle of 

 the seventeenth century. Notwithstand- 

 ing the frequent citation of the phrase, 



