iv PREFACE. 
single germ, or from a few germs It would 
seem, from the frequency with which this notion 
is revived, — ever returning upon us with hydra- 
headed tenacity of life, and presenting itself 
under a new form as soon as the preceding one 
has been exploded and set aside, — that it has a 
certain fascination for the human mind. This 
arises, perhaps, from the desire to explain the 
secret of our own existence; to have some sim- 
ple and easy solution of the fact that we live. 
I confess that there seems to me to be a repul- 
sive poverty in this material explanation, that is 
contradicted by the intellectual grandeur of the 
universe ; the resources of the Deity cannot be so 
meagre, that, in order to create a human being 
endowed with reason, he must change a monkey 
into a man. This is, however, merely a personal 
opinion, and has no weight as an argument; nor 
am I so uncandid as to assume that another may 
not hold an opinion diametrically opposed to mine 
in a spirit quite as reverential as my own. But I 
nevertheless insist, that this theory is opposed to 
the processes of Nature, as far as we have been 
able to apprehend them; that it is contradicted 
by the facts of Embryology and Paleontology, 
the former showing us norms of development as 
