CONTENTS. Xlll 



§ 3. Structure of sperm — i'age 



_ '' Head," " tail," "middle portion," &c. 

 § 4. Physiology of sperm — 



Locomotor energy and persistent vitality. 

 §5. Origin of sperm — 



Theory of spermatogenesis. 

 § 6. Further comparison of sperm and ovum — 



Processes comparable with formation of polar 

 globules. 

 § 7. Chemistry of the sperm. 



CHAPTER X. 



Theory of Sex : Its Nature and Origin - - - 11 7-134 



§. I. Suggested theories of male and female — 



Rolph. 



Minot. 



Brooks. 

 § 2. Nature of sex — seen in Sex-cells. 



The cell-cycle. 

 Protoplasmic interpretation. 

 § 3. Problem of origin of sex. 

 § 4. Incipient sex among plants. 

 § 5. Incipient sex among animals. 

 § 6. Corroborative illustrations. 

 § 7. General conclusions from foregoing chapters. 



BOOK III.— PROCESSES OK REPRODUCTION. 



CHAPTER XL 



Sexual Reproduction . . . . - 137-156 



§ I. Different modes of reproduction. 



§ 2. Facts involved in sexual reproduction. 



§ 3. Fertilisation in plants — 



P'rom Sprengel to Strasburger. 

 § 4. Fertilisation in higher animals — 



From Martin Barry and Biitschli, to Van Bene- 

 den and Boveri. 

 § 5. Fertilisation in Protozoa. 

 § 6. Origin of fertilisation — 



{a.) Plasmodium. 



(d.) Multiple conjugation. 



{c.) Ordinary conjugation. 



{d.) Union of incipiently dimorphic cells. 



{e.) Fertilisation by differentiated sex-cells. 

 § 7. Hybridisation in animals and plants. 



