Notes on Hybridization, by Francis Day, C.1.E. and F.L.S. 
During the present century the hybridization of animals and 
plants in this country has received more attention than at any 
previous period, although possibly to a far less extent than the 
interest and importance of the subject deserves, while it has 
been admitted by most of our zoologists that many of the 
assertions which formerly passed current as facts have been 
ascertained to be partially or wholly erroneous. Thus there 
are few, if any, at the present day who could admit the theory 
of Ray, that “any two animals that can procreate together, and 
whose issue can procreate, are specifically the same,” nor the 
statement of the elder Flourens that hybrids can only be 
produced between individuals of the same genus. “ Constant 
fertility in the hybrid, proved, in the opinion of Hunter, that 
the parents were varieties of the same and not of distinct 
species (Owen, Proceedings Zoological Society, 1836, page 85); 
while Darwin observed that “species belonging to distinct 
genera can rarely, and those belonging to distinct families can 
never, be crossed.” Newton (l.c. 1860 p. 338) asserted, when 
treating of hybrid ducks, “ that although the hybrid offspring 
of two animals, clearly distinct, may of themselves be perfectly 
fertile, it is not proved that this fertility extends to a second 
generation.”” Romanes (Encyclopedia Britannica, 9th or present 
edition, article “ Hybridism’’) has gone still further, remarking 
that it is doubtful whether there is a single instance of a 
perfectly fertile hybrid, having emanated from a cross between 
two animal species.”” He concluded his article with the 
following words; “On the subject of animal hybrids there is 
