the immense amount of its eggs destroyed by foxes; but he adds that the parasitic fungi which periodically infest it are a far more terrible enemy than any bird, because they destroy the moth over very large areas at once. As to various species of mice (Mus sylvaticus, Arvicola arvalis, and A. agrestis), the same author gives a long list of their enemies, but he remarks: "However, the most terrible enemies of mice are not other animals, but such sudden changes of weather as occur almost every year." Alternations of frost and warm weather destroy them in numberless quantities; "one single sudden change can reduce thousands of mice to the number of a few individuals." On the other side, a warm winter, or a winter which gradually steps in, make them multiply in menacing proportions, notwithstanding every enemy; such was the case in 1876 and 1877.(37) Competition, in the case of mice, thus appears a quite trifling factor when compared with weather. Other facts to the same effect are also given as regards squirrels. As to birds, it is well known how they suffer from sudden changes of weather. Late snow-storms are as destructive of bird-life on the English moors, as they are in Siberia; and Ch. Dixon saw the red grouse so pressed during some exceptionally severe winters, that they quitted the moors in numbers, "and we have then known them actually to be taken in the streets of Sheffield. Persistent wet," he adds, "is almost as fatal to them." On the other side, the contagious diseases which continually visit most animal species destroy them in such numbers that the losses often cannot be repaired for many years, even with the most rapidly-multiplying animals. Thus, some sixty years ago, the sousliks suddenly disappeared in the neighbourhood of Sarepta, in South-Eastern Russia, in consequence of some epidemics; and for years no sousliks were seen in that neighbourhood. It took many years before they became as numerous as they formerly were.(38)