The Making of Species 
over-rate small differences when drawing up a 
classification. It would be therefore safe to say, 
in the present state of our knowledge, that species 
belonging to different natural families cannot 
hybridize. 
In some cases multiple hybrids have been 
produced. Thus, at the London Zoological 
Gardens, many years ago, a hybrid between the 
Gayal of India (Bos frontahs) and the Indian 
humped cow mentioned above was put to an 
American bison, and produced a double hybrid 
calf. 
M. G. Rogeron of Angers bred many hybrids 
from a male pochard and a duck bred from a 
Mallard and a Gadwall. 
More recently, Mr J. L. Bonhote has suc- 
ceeded in combining the blood of five wild species 
of ducks in one individual. 
Mr J. T. Newman has also bred turtle-doves 
containing the blood of three distinct species. 
A cross, which usually results in sterile 
offspring, may in very rare cases produce a fertile 
individual ; thus, Mr A. Suchetet once succeeded 
in obtaining a three-quarter-bred bird from the 
not uncommon hybrid of the tame pigeon and 
tame collared dove (Zurtur risorius), which is 
usually barren, by pairing it with a dove; but the 
bird thus produced, when again paired with a 
dove, was itself sterile. 
Some of the cases here given seem to encourage 
126 
