And, again, when he says:-- "From the opportunities we have enjoyed in the examination of the varieties and species of domesticated quadrupeds and birds, we have never found any difficulty in deciding on the species to which these varieties belong." Those of us who are still groping in darkness certainly have a right to ask who are the authorities alluded to, and what are those "characters which distinguish and separate species" as distinctly and infallibly as "genera?" They are certainly not in print. The doctor must pardon us for reminding him that there is printed evidence that his own mind is not always free from doubts. In the introduction of Audubon and Bachman's _Quadrupeds of America_, p. vii., it is said:-- "Although _genera_ may be easily ascertained by the forms and dental arrangements peculiar to each, many _species_ so nearly approach each other in size, while they are so variable in color, that it is exceedingly difficult to separate them with positive certainty." Again, in speaking of the genus _vulpes_ (foxes), the same work says:-- "The characters of this genus differ so slightly from those of the genus _canis_, that we are induced to pause before removing it from the sub-genus in which it had so long remained. As a general rule, we are obliged to _admit that a large fox is a wolf, and a small wolf may be termed a fox_. So inconveniently large, however, is the list of species in the old genus _canis_, that it is, we think, advisable to separate into distinct groups such species as possess any characters different from true wolves." Speaking of the origin of the domestic dog, Dr. Bachman, in his work on _Unity of Races_, p. 63, says:-- "Notwithstanding all these difficulties--and we confess we are not free from some doubts in regard to their identity (dog and wolf)--if we were called upon to decide on any wild species as the progenitor of our dogs, we would sooner fix upon the large wolf than on any other dog, hyena, or jackal," &c. The doctor is unable, here at least (and we can point out many other cases), to "designate species;" and the recent investigations of Flourens, at the _Jardin des Plantes_, prove him wrong as regards the origin of the dog. The dog is not derived from the "large wolf," but, with it, produces hybrids, sterile after the third generation. The dog forms a genus apart.