| → period co-extensive with the world. 1859 1860 1861 1866 |
| period— Alternate Glacial periods in the North and South. 1869 1872 |
|
| → northern parts where the circumpolar land is almost continuous, 1859 1860 1861 1866 1869 |
| arctic and northern temperate parts, 1872 |
|
| → for it is a most rare case to find a group of organisms confined to any small spot, having conditions peculiar in only a slight degree; for instance, 1859 1860 1861 1866 |
| No doubt 1869 1872 |
|
|
CHAPTER
|
| GEOGRAPHICAL DISTRIBUTION. |
| Present distribution cannot be accounted for by differences in physical conditions— Importance of barriers— Affinity of the productions of the same continent— Centres of creation— Means of
by changes of climate and of the level of the land, and by occasional means— Dispersal during the Glacial
→period co-extensive with the world.
|
| IN considering the distribution of organic beings over the face of the globe, the first great fact which strikes us is, that neither the similarity nor the dissimilarity of the inhabitants of various regions can be
for
climatal and other physical conditions. Of late, almost every author who has studied the subject has come to this conclusion. The case of America alone would almost suffice to prove its
for if we exclude the
→northern parts where the circumpolar land is almost continuous,
all authors agree that one of the most fundamental divisions in geographical distribution is that between the New and Old Worlds; yet if we travel over the vast American continent, from the central parts of the United States to its extreme southern point, we meet with the most diversified conditions;
humid districts, arid deserts, lofty mountains, grassy plains, forests, marshes, lakes, and great rivers, under almost every temperature. There is hardly a climate or condition in the Old World which cannot be paralleled in the New— at least as closely as the same species generally
→for it is a most rare case to find a group of organisms confined to any small spot, having conditions peculiar in only a slight degree; for instance,
|
