Transcriber's Note:Minor typographical errors have been corrected without note.Punctuation and spelling were made consistent when a predominant form was found in this book; otherwise they were not changed.Ambiguous hyphens at the ends of lines were retained.Mid-paragraph illustrations have been moved between paragraphs and some illustrations have been moved closer to the text that references them."... the shells of the eggs in class Aves."* (Page 152.) A footnote is indicated but missing from the text.The Contents table was added by the transcriber.