I wish that dedications were still in vogue, so that these pages could be inscribed to all those many friends whose unfailing kindness and courtesy made my visit to the United States so pleasant, when the substance of this volume was delivered as a Lowell Course at Boston, and as lectures in New York, Chicago, and other university centres, during the early part of this year. The reader will doubtless be glad to learn that further observations — and they are much needed — ou habit and instinct will probably form part of Prof. Whitman's work at an experimental station in connection with the Bio logical Department of Chicago University. Similar observations might also be prosecuted with advantage in some of our own zoological gardens, as was the earnest wish of George Romanes, to whose in?uence and encourage ment I am, like many others, so deeply indebted.