The species are taken up in groups, in so far as this can be done safely. Each biography, of which there are 119, is, as a rule, a composite applying to a number of near-related forms, thus simplifying matters of presentation, and avoiding repetition. A marked feature of the book is the degree of concentration attained; there is no trace of padding, and no room for baseless speculation, sentimentalizing or humanizing, such as characterize many current “nature” books. At the same time the style is animated and thoroughly entertaining, a gift of composition which Nelson has exercised in many preceding contributions. Here is an instance, unfortunately a rare one, in which a man who really knows the field has put out a popular book on a natural history subject. Many are the portrayals which are evidently based on Nelson’s own personal field knowledge, some of them involving facts here for the first time made known to science. His account of the behavior of kangaroo rats in Lower California is particularly apt in illustration of the above statement. During several nights I passed hours watching at close range the habits of these curious animals. As I sat quietly on a mess box in their midst ... [they] would forage all about with swift gliding movements, repeatedly running across my bare feet. Any sudden movement startled them and all would dart away for a moment, but quickly return.... They were so intent on the food [grains of rice put out for them] that at times I had no difficulty in reaching slowly down and closing my hand over their backs. I did this dozens of times, and after a slight struggle they always became quiet until again placed on the ground, when they at once renewed their search for food as though no interruption had occurred.... While occupied in this rivalry for food they became surprisingly pugnacious. If one was working at the rice pile and another rat or a pocket mouse approached, it immediately darted at the intruder and drove it away. The mode of attack was to rush at an intruder and, leaping upon its back, give a vigorous downward kick with its strong hind feet.... Sometimes an intruder, bolder than the others, would run only two or three yards and then suddenly turn and face the pursuer, sitting up on its hind feet like a little kangaroo. The pursuer at once assumed the same nearly upright position, with its fore feet close to its breast. Both would then begin to hop about watching for an opening. Suddenly one would leap at the other, striking with its hind feet, ... [producing] a distinct little thump and the victim rolled over on the ground. After receiving two or three kicks the weaker of the combatants would run away. The thump made by the kick when they were fighting solved the mystery which had covered this sound heard repeatedly during my nights at this camp.