In his investigation of the habits of squirrels, he finds the red squirrel, or chickaree, much more intelligent than the chipmunk. The latter is easily trapped, but the former profits by experience and is rarely secured a second time. These little creatures are also adepts in feigning. Two examples are cited in which squirrels apparently ill recovered rapidly when left alone and made their escape in vigorous fashion. Many instances of animals shamming death are judged to be cases of catalepsy induced by excessive fear. The chickaree is also credited with some musical capacity, one being observed, when excited, to utter tones that were birdlike; whence it is concluded "likely that throughout the order _Rodentia_ a genuine musical appreciation exists, and considerable ability in expressing states of emotion by vocal forms." While experimenting with hibernating animals, Professor Mills kept a woodchuck in confinement five years, and noted that it had a drowsy or torpid period from November to April. Another specimen subjected to the same conditions did not hibernate for an hour during the entire season. Bats began to hibernate at 45° to 40° F., and were so affected by temperature that they could be worked like a machine by varying it. The woodchuck, however, was comparatively independent of heat and cold, but very sensitive to storms. This is found to be true of many wild animals, that they "have a delicate perception of meteorological conditions, making them wiser than they know, for they act reflexly." Some records are given of cases of lethargy among human beings, and in regard to these, as well as normal sleep and hibernation, it is suggested that their conditioning and variability throw great light upon the evolution of function. In order to observe closely the psychic development of young animals, Professor Mills raised families of dogs, cats, chickens, rabbits, guinea-pigs, and pigeons. The data obtained by him, given in the form of diaries with comparisons and conclusions, constitute Part III, the larger half of the book, unquestionably first in importance and interest. It is scarcely possible to overvalue careful studies like these, undertaken not to justify theories, but to bring to light whatever truths may be apprehended of the nature of growth and connection of mind and body. The last division of the book contains the discussions on instinct by Professors Mills, Lloyd Morgan, Baldwin, and others, first published in Science. The beginning of the volume, devoted to a general consideration of the subject, consists of papers on methods of study and comparative psychology which have appeared in various scientific periodicals, including this magazine. GENERAL NOTICES.