To relate it to the theory of evolution Cott concludes that selective pressure by predators seems to have forced vulnerable species along two divergent lines of specialization: leading in those which are relatively palatable toward concealment, and in those which are relatively distasteful toward advertisement. HOW MANY FEATHERS HAS A BIRD? [Illustration] The question as to the number of feathers on a bird seems a simple one without complication. Dr. Wetmore, the well-known ornithologist who was secretary of the Smithsonian Institute, has given us some data. The number varies with the species, of course: the smallest bird, a hummingbird from Cuba, had the fewest, 940 feathers; larger birds had more, the robin 2587, and the mourning dove 2635 feathers. A glaucous-winged gull had 6540; a mallard 11,903 feathers; a Plymouth Rock chicken was said to have 8325 feathers; and a later investigator reported 25,216 feathers on a swan. But as one thinks of it, more questions arise, as in any investigation. The answer to one question poses two more. The first question is, do not the birds in winter need a wanner plumage to keep out the cold than they do in summer, when it is warm? Do they have more feathers then? This was definitely true in the case of the goldfinch: a bird in summer dress had only 1439 feathers, while one in winter plumage had 2368 feathers, obviously an adaptation for cold weather. The next question is more abstruse, but eminently practical: the smaller a body, the larger exposed surface for its weight it presents. That is, for its weight a small bird has a proportionately much greater surface from which heat is lost than does a larger one. With equal heat-producing mechanism and metabolism, a small bird would need more insulation than a large one. Reduced to its simplest: one would expect small birds to have relatively more feathers than large ones: more feathers per gram of weight. Is this true? Two members of the Department of Poultry Husbandry at Cornell University, Dr. F. B. Hutt and Lelah Ball, supplied the answer. Small birds do have more feathers per gram of body weight than do larger ones. A hummingbird weighing 2.8 grams had 940 feathers or 335 feathers per gram; a nighthawk weighing 67.9 grams had 2034 feathers or 29 feathers per gram; while a swan weighing 6123 grams had 25,216 feathers or 4 feathers per gram of body weight. Presumably there are still other relations: Do the birds that live in the tropics where it is warm have fewer feathers than species of the same size of arctic climates, as one would expect? Are certain types of feathers such as those of aquatic birds better insulated than those of land birds, so that the bird requires fewer of them to keep warm? Does a dense coat of down reduce the number of feathers needed to keep warm? Do the loose feathers of ostriches, lacking barbules, necessitate some adjustment in numbers? The things we've learned point the way to other questions to be investigated.