This is an OCR edition without illustrations or index. It may have numerous typos or missing text. However, purchasers can download a free scanned copy of the original rare book from GeneralBooksClub.com. You can also preview excerpts from the book there. Purchasers are also entitled to a free trial membership in the General Books Club where they can select from more than a million books without charge. Original Published by: The Macmillan Co. in 1907 in 493 pages; Subjects: Variation (Biology); Hybridization; Sex; Zoology; Sex determination, Genetic; Zoology, Experimental; Health & Fitness / Sexuality; Psychology / Human Sexuality; Religion / Sexuality & Gender Studies; Science / Life Sciences / Biology / General; Science / Life Sciences / Genetics & Genomics; Science / Life Sciences / Zoology / General; Self-Help / Sexual Instruction;