CONTENTS. ix 



PAGE 



III. Structure of sperm — 



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



IV. Physiology of sperm — 



Locomotor energy and persistent vitality. 

 V. Origin of sperm — 



Theory of spermatogenesis. 

 VI. Further comparison of sperm and ovum — 



Processes comparable with formation of polar 

 globules. 

 VII. Chemistry of the sperm. 



CHAPTER X. 



Theory of Sex : lis Nature and Origin - - - - - iu-126 

 I. Suggested theories of male and female — 

 Rolph. 

 Minot. 

 Brooks. 

 II. Nature of sex — seen in Sex-cells. 



The cell-cvcle. 



Protoplasmic interpretation. 



III. Problem of origin of se 



IV. Incipient sex among plants. 

 V. Incipient sex among animals. 



VI. Corroborative illustrations 



VII. General conclusions from foregoing chapters 



BOOK III.— PROCESSES OF REPRODUCTION. 



CHAPTER XI. 



Sexual Reproduction -. - 129-146 



I. Different modes of reproduction, v^ 

 II. Facts involved in sexual reproduction. ^C 



III. Fertilization in plants — 



From Sprengel to Strasburger. 



IV. Fertilization in higher animals - 



From Martin Barry and Biitschli, to Van Bene- 

 den and Boveri. 

 V. Fertilization in Protozoa. 

 VI. Origin of fertilization — 



(a) Plasmodium. 



(b) Multiple conjugation. 



(c) Ordinary conjugation. 



(d) Union of incipiently dimorphic cells. 



(e) Fertilization by differentiated sex-cells. 

 VII. Hybridization in animals and plants. 



