of Edinburgh, Session 1864 - 65 . • 285 
11 ate in reversion to the original type. Now here again we have 
the emphatic declaration of Mr Grould, that among the thousands 
of specimens which have passed through his hands, from all the 
genera of this great family, he has never seen one case of mixture 
or hybridism between any two species, however nearly allied. But 
this passage is so important, that I quote it entire. “ It might be 
thought by some persons that four hundred species of birds so dimin- 
utive in size, and of one family, could scarcely be distinguished 
from each other ; but any one who studies the subject, will soon per- 
ceive that such is not the case. Even the females, which assimi- 
late more closely to each other than the males, can be separated 
with perfect certainty ; nay, even a tail-feather will be sufficient for 
a person well versed in the subject to say to what genus and species 
the bird from which it has been taken belongs. I mention this 
fact to show that what we designate a species has really distinctive 
and constant characters ; and in the whole of my experience, with 
many thousands of humming-birds passing through my hands, I 
have never observed an instance of any variation which would lead 
me to suppose that it was the result of a union of two species. I 
write this without bias, one way or the other, as to the question of 
the origin of species. I am desirous of representing Nature in her 
wonderful ways as she presents herself to my attention at the close 
of my work, after a period of twelve years of incessant labour, and 
not less than twenty years of interesting study.”* 
If, therefore, new species are born from the old, it is not by acci- 
dental mixture ; it is not by the mere nursing of changes advan- 
tageous in the battle of life ; it must be from the birth of some one 
couple, male and female, whose organisation is subjected to new 
conditions corresponding with each other, and having such force of 
self-continuance, as to secure it against reversion. It matters not 
how small the difference may be from the parent form ; if that 
difference be constant, and if it be associated with some difference 
equally constant in the female form, it becomes at once a new 
species. There are some cases mentioned by Mr Grould which may 
possibly be examples of the first founding of a new species. In 
the beautiful genus “ Cynanthus,” he tells us that there are some 
* Gould’s “ TrochilicliB,” Introduction. 
