The nests occupied as summer homes are placed in shallow burrows a few inches below the surface of the ground, or they may be in a hollow tree, under a piece of bark, in a dense tussock of grass, or in other makeshift shelter. In these nests the young, varying from two to eight in number, are born at varying times between May and September, indicating the probability that more than one litter is produced each season. When suddenly startled from her nest the female often flees with several of the young clinging to her teats. She runs swiftly through the grass, and if hard pressed will take a long leap, still carrying the pendant young. It is surprising that such delicately formed animals can make long leaps in thickly grown places and apparently land safely, especially when carrying their young. In the flights of the mother some of the young must be jarred loose, but when the alarm is over no doubt she returns to find and rescue any that may be missing. In the northeastern States jumping mice are common habitants of meadows. They are equally at home in the rocky meadows of New England, on the flower-spangled borders of rushing trout streams in the Sierra Nevada of California, and the boggy glades of subarctic Alaska. My first acquaintance with them was made many years ago, during haying time, in northern New York. Hidden under a haycock, as the last forkful was raised one of them was often revealed, and its startling leaps always resulted in an exciting chase, which usually ended in the escape of the strange little beast. Unlike most of their small fellows of meadow and thicket, jumping mice regularly hibernate, occupying the nests near the bottoms of the winter burrows. They usually become fat on the abundance of food at the end of summer, and in September or October, with the approach of cool weather, enter their winter quarters and sink into the long, hibernating lethargy. Sometimes two of them are found hibernating in the same nest. During hibernation they are coiled up in little furry balls, the nose resting on the abdomen, the hind feet on each side of the head, and the tail wound around the body. The winter sleep usually lasts until spring, but may be broken at any time by mild weather. When hibernating the mice appear cold and lifeless, but if one is carried into a warm house or even held a long time in the captor’s hands it will slowly awaken and may become as lively as in summer. When returned to a low temperature, however, it soon resumes its mysterious seasonal sleep. =THE SILKY POCKET MICE= (=Perognathus flavus= and its relatives) (_For illustration, see page 515_)