PREFACE. I FEEL that the printing of my lectures brings with it a certain difficulty. Lectures intended to be read within the Museum, with a continual reference, implied and often expressed, to the place, the objects gathered within it and their associations, must have had a certain fifaess which will be more or less diminished when they come to be read under different conditions. Moreover, they were written and spoken with an idea always present in my mind that I had a class of students whom I was addressing, and that my other auditors stood in a more remote relation to me. Certain appeals to my teaching, certain dlusions to the practice of the students and to their position of relative de- pendence and inferiority of age or acquaintance with the world, of little or no significance to my readers, are thus explained. I have not seen any way of so modifying these lectures as to suit my feelings and wishes in the present nor could I have found the time to do so had I seen my way clearly...