CONTENTS. xi 



Pages 

 Sexual selection operating as between different spermato- 



zoids. Movements of the female element. Vegetable 

 fecundation. Progressive differentiation of the two sex- 

 ual elements. Sexual reproduction of the Ectocarpus sili- 

 culosus, after Berthold. Investigations of Pfeffer upon 

 the spermatozoids of cryptogams. Action of certain 

 chemical excitants upon these elements. Specific charac- 

 ter of the excitant. The threshold of excitation. Appli- 

 tion of Weber's law 75~9i 



THE PHYSIOLOGICAL FUNCTION OF THE 

 NUCLEUS. 



Functions attributed to the protoplasm and to the envelop- 

 ing membrane. The nucleus, its histological importance 

 proved by the phenomena of caryokinesis. Balbiani and 

 Gruber have, at times, observed Infusoria and Actinophrys 

 deprived of nuclear substance. Nussbaum's and Gruber's 

 experiments of vivisection upon the Stentor cceruleus. 

 Fragments provided with nucleus reconstruct themselves. 

 Experiments of Balbiani Facts observed by Gruber, 

 in general, confirmed. Error of Gruber respecting frag- 

 ments without nucleus. These fragments do not con- 

 tinue to live, their plasma undergoes disorganization. 

 Experiments of division. Experiments made upon 

 Infusoria while in conjugation. The presence of the 

 old nucleus in a severed fragment only brings about 

 an incomplete regeneration. The nucleus presides over 

 all physiological functions, the totality of which con- 

 stitutes life. The regenerative and reproductive property 

 of the plasma is lost before the psychical functions are. 

 Agreement of all these facts with the phenomena ob- 

 served as taking place during the spontaneous division of 

 Micro-organisms 92-105 



IX. 



CONCLUSION. 



Statement of M. Richet's position respecting cellular psy- 

 chology 105 



