Brewster oh Helminthoph'Xga leu co b ro n ch ia l is . 223 
the case of No. 4,667 — reproduce with at least one, and prob- 
ably either of the parent species; if not — as is by no means 
impossible — -with each other. But the case is not without 
precedent. As long ago as 1847, Dr. Samuel George Morton, 
in the course of an essay on the subject of hybridity* cited 
.several well-authenticated instances of the interbreeding — often in 
a wild state — of various European Finches. A yet more remote 
alliance, given on the authority of M. Vieillot, was that of a 
Canary and a Nightingale, the single egg resulting from their 
union proving, however, unfertile. Among his conclusions the 
following are especially pertinent to the above connection : 
“1. A latent power of hybridity exists in many animals in 
the wild state, in which state, also, hybrids are sometimes pro- 
duced. 
“2. Hybridity occurs not only among different species, but 
among different genera ; and the cross-breeds have been prolific 
in both cases. 
“3. Domestication does not cause this faculty, but merely 
evolves it.” 
The Rev. John Bachman subsequently took the matter upf and 
supported the negative side of the question, but while be severely 
criticised Dr. Morton’s views we find him admitting (p. 169), 
u That in a very few species a progeny has been produced that 
was incapable of propagating with the half-breeds, — in other 
words, that the hybrid male was physically incapable of having 
offspring with a hybrid female ; hence the latter had to resort to 
the full blood of either species, and thus the intermediate breed 
returned to one or the other of the original species.” 
In the latter fact we doubtless have the explanation of such 
aberrant specimens as Nos. 1,210 and 2,620, which unmistakably 
exhibit a slight and otherwise unaccountable trace of hybrid 
parentage ; and similarly it is not unlikely that the yellow breast 
of occasional specimens of chrysoptera may be due to a taint of 
pinus blood. The impaired sexual vitality — granting, for the 
* “ Hybridity in Animals and Plants considered in reference to the Question of the 
Unity of the Human Species.” American Journal of Science and Arts, 2d Ser., Vol. 
Ill, 1847, pp. 203-21 1. 
f An Investigation of the Cases of Hybridity in Animals on Record, considered in 
reference to the Unity of the Human Species. Am. Journ. Sci. and Arts, 2d Ser., 
Vol. V, 1848, pp. 168-197. 
