Excerpt from A History of British Birds, Vol. 1: With Illustrations of Their Eggs Interbreeding may or may not mean cross-breeding. Wherever the interbreeding which habitually takes place between the individuals of a species has not ceased, any differences between them can only be subspecific. Subspecies may be defined as groups in which the interbreeding which habitually takes place between individuals in a Species has not yet ceased, but takes place along the whole line of its geographical distribution, though seldom between the two extremes. About the Publisher Forgotten Books publishes hundreds of thousands of rare and classic books. Find more at www.forgottenbooks.com This book is a reproduction of an important historical work. Forgotten Books uses state-of-the-art technology to digitally reconstruct the work, preserving the original format whilst repairing imperfections present in the aged copy. In rare cases, an imperfection in the original, such as a blemish or missing page, may be replicated in our edition. We do, however, repair the vast majority of imperfections successfully; any imperfections that remain are intentionally left to preserve the state of such historical works.