the lessened fertility of crossed forms is an infallible criterion of
specific distinctness. Anyhow these animals keep distinct in the countries
which they inhabit in common. On the other hand, all domestic dogs, which
are here supposed to be descended from several distinct species, are, as
far as is known, mutually fertile together. But, as Broca has well remarked
(1/45. 'Journal de la Physiologie' tome 2 page 385.), the fertility of
successive generations of mongrel dogs has never been scrutinised with that
care which is thought indispensable when species are crossed. The few facts
leading to the conclusion that the sexual feelings and reproductive powers
differ in the several races of the dog when crossed are (passing over mere
size as rendering propagation difficult) as follows: the Mexican Alco
(1/46. See Mr. R. Hill's excellent account of this breed in Gosse's
'Jamaica' page 338; Rengger 'Saugethiere von Paraguay' s. 153. With respect
to Spitz dogs, see Bechstein's 'Naturgesch. Deutschlands' 1801 b. 1 s. 638.
With respect to Dr. Hodgkin's statement made before Brit. Assoc. see 'The
Zoologist' volume 4 for 1845-46 page 1097.) apparently dislikes dogs of
other kinds, but this perhaps is not strictly a sexual feeling; the
hairless endemic dog of Paraguay, according to Rengger, mixes less with the
European races than these do with each other; the Spitz dog in Germany is
said to receive the fox more readily than do other breeds; and Dr. Hodgkin
states that a female Dingo in England attracted the male wild foxes. If
these latter statements can be trusted, they prove some degree of sexual
difference in the breeds of the dog. But the fact remains that our domestic
dogs, differing so widely as they do in external structure, are far more
fertile together than we have reason to believe their supposed wild parents
would have been. Pallas assumes (1/47. 'Acta Acad. St. Petersburgh' 1780
part 2 pages 84, 100.) that a long course of domestication eliminates that
sterility which the parent-species would have exhibited if only lately
captured; no distinct facts are recorded in support of this hypothesis; but
the evidence seems to me so strong (independently of the evidence derived