The few remaining days of August passed, and September came, bringing little suggestion of autumn rains or coolness. Dr. and Mrs. Marvin had joined them, and the former's interest in every wild creature of the woods became infectious. Alf and Fred were his ardent disciples, and he rarely found an indifferent listener in Amy. The heat of the day was given up to reading and the fashioning of alpenstocks, and the mornings and late afternoons to excursions. In one of these they had sat down to rest near an immense decaying tree that was hollow in parts, and full of holes from the topmost shattered branches to the ground. "That," said the doctor, "might fitly be called an old tenement-house. You have no idea how many and various creatures may have found a home in it." He was immediately urged to enumerate its possible inhabitants in the past, present, and future. The doctor, pleased with the conceit of regarding the decaying tree in this light, began with animation: "All three of the squirrels of this region have undoubtedly dwelt in it. I scarcely need do more than mention the well-known saucy red or fox squirrel, whose delight is mischief. By the way, we have at home two tame robins that before they could fly were tumbled out of their nest by one of these ruthless practical jokers. The birds come in and out of the house like members of the family. The graceful gray squirrel is scarcely less familiar than the red one. He makes a lively pet, and we have all seen him turning the wheel attached to his cage. The curious little flying-squirrel, however, is a stranger even to those to whom he may be a near neighbor, for the reason that his habits are chiefly nocturnal. He ventures out occasionally on a cloudy day, but is shy and retiring. Thoreau relates an interesting experience with one. He captured it in a decayed hemlock stump, wherein it had a little nest of leaves, bits of bark, and pine needles. It bit viciously at first, and uttered a few 'dry shrieks,' but he carried it home. After it had been in his room a few hours it reluctantly allowed its soft fur to be stroked. He says it had 'very large, prominent black eyes, which gave it an innocent look. In color it was a chestnut ash, inclining to fawn, slightly browned, and white beneath. The under edge of his wings (?) tinged yellow, the upper dark, perhaps black.' He put it into a barrel, and fed it with an apple and shag-bark hickory-nuts. The next morning he carried it back and placed it on the stump from which it had been taken, and it ran up a sapling, from which it skimmed away to a large maple nine feet distant, whose trunk it struck about four feet from the ground. This tree it ascended thirty feet on the opposite side from Thoreau, then, coming into view, it eyed its quondam captor for a moment or two, as much as to say 'good-by.' Then away it went, first raising its head as if choosing its objective point. Thoreau says its progress is