2 
ZOOLOGICAL LITERATURE. 
volume is devoted to general considerations founded on the 
materials treated of in the first ; the causes and laws of varia- 
bility are discussed, inheritance and its laws, crossing, sterility 
from a changed condition of life and close interbreeding — and the 
coefficient selection by man, methodical or unconscious. Finding 
that these subjects, as well as the several modes of reproduction, 
stand in some sort of relation to each other, and ought to be 
connected by a tangible method, Mr. Darwin advances the 
hypothesis of Pangenesis,^^ which implies that the whole orga- 
nization, in the sense of every separate atom or unit, reproduces 
itself. 
It will be evident from these remarks that the work before 
us would be more properly referred to in a record on general 
zoology than in one on Mammalia. Nevertheless, although it 
is written with reference to a particular theory, the mammalo- 
gist will find such an amount of facts relating to the domesti- 
cated Mammalia, gathered in a connected form, that especially 
the first volume will prove to be of the highest interest and 
most instructive even to specialists, the more so as the author 
states the facts favourable or opposed to his theory with equal 
impartiality. We cannot enter into the details of His accounts 
of the several species within the narrow limits of this notice, 
the author omitting nothing in the history, geographical distri- 
bution, zoological and anatomical characters of each animal and 
its races which could throw light upon its origin ; and we must 
be satisfied to mention here that he concludes that dogs, cats, 
pigs, oxen, sheep, and goats have descended from several wild 
species, whilst horses, asses, and rabbits are each derived from a 
single species only. 
Wagner, M. Die Darwin^schc Thcoric und das Migrations- 
gesetz der Organismen. Leipzig, 1868. 8vo, pp. 62. 
The author argues that natural selection by itself does not 
account for the origin of new varieties or species, but that it 
must be preceded by a migration (active or passive) of indivi- 
duals from their original habitat, and that such colonists must 
remain separated from the typical stock for a considerable time, 
in order to allow the greater or less amount of inherent varia- 
bility to be developed by and adapted to the new external con- 
ditions, without being interfered with by constant interbreeding 
with the old type. 
A paper by the same author in Sitzgsber. Bayr. Ak. Wiss. 
1868, i, pp. 359-395, is merely preliminary to the present more 
detailed publication. 
Brandt, J. F. Zoogeographische und Palaeontologische Bei- 
trage. Verhandl. mineral. Gesellsch. St. Petersb. ii. Also 
separately printed, St. Petersb. 1867, 8vo, pp. 258. 
We have referred to these important contributions in Zool, 
