1877.] Recent Literature. 233 
of Geographical Mutations. IV. Geographical Zoölogy; a Systematic 
Sketch of the Chief Families of Land Animals in their Geographical 
Relations. - 
The grand merit of the work, and one which will give a substantial 
foundation to the author’s fame as a biologist, aside from his authorship, 
simultaneous with Darwin, of the doctrine of natural selection, is the 
endeavor to account, from a more extended range of study than any pre- 
vious author, for the present diversity of life on the different continents, by 
a study of the fossil forms and of past geological changes. He discards the 
older notions of certain authors, as Humboldt, Schouw, and others, that the 
distribution of life over the globe is due primarily to differences in tem- 
perature and to physical barriers. In how broad a way our author has 
treated this subject may be seen by the chapter entitled Summary of the 
Past Changes and General Relations of the Several Regions, reprinted 
in the last number of this journal. As long ago as 1847 Agassiz stated 
in his Introduction to the Study of Natural History that “ modification 
of types [on different continents was] not caused by climate,” though he 
proposed no scientific explanation as to how they did originate. Mr. 
Wallace supposes that all land animals originated in the northern portion 
of the Europe-Asiatic continent, and thence migrated south into India, 
Australasia, Africa, and to North America by means of a supposed for- 
mer polar continent of which Arctic America, Greenland, Iceland, Spitz- 
bergen, and Nova Zembla are the remnants. South America, he suggests, 
was peopled from North America. This view we suppose to be original 
with the author, and the hypothesis seems to be supported by known palæ- 
ontological facts, and may serve as a working theory until a better one 1s 
offered. Mr. Wallace’s view that the primitive centre of distribution was 
in the Old World is based on the fact that life is more abundant and the 
continental mass larger than that of North America. Mr. Wallace quite 
thoroughly disposes of the notion, advanced by Heer, Murray, and others, 
of continental bridges, and fully recognizes the facts strenuously main- 
tained for years by Dana and others, and proven by the late deep sea 
explorations, that the present ocean beds have always been such," oscil- 
lations of the original continental masses and the evident former exist- 
ence of an arctic Americo-European continent being sufficient to account 
for the regular and normal interchange of life, which paleontology shows 
Must actually have occurred. 
_ The limits of the six primary regions into which the earth’s surface 
1s divided by our author have been marked out by geological agencies 
1 “ The preliminary studies above enumerated will, it is believed, enable us to see 
the bearing of many facts in the distribution of animals, that would otherwise be in- 
ae continents and oceans, probably the most permanent features of our globe.” 
ol. i., p- 9.) 
