390 SYNOPSIS 



II. BIOGENESIS. 



PAGE 



a. Definition of biogenesis and abiogenesis : brief history of 



the controversy .... 93 



b. Crucial experiment with putrescible infusions : sterilization : 



germ-filters : occurrence of abiogenesis disproved under 

 known existing conditions ... 96 



III. HOMOGENESIS. 



Definition of homogenesis and heterogenesis : truth of the 



former firmly established .... 100 



IV. ORIGIN OF SPECIES. 



a. Meaning of the term Species : the question illustrated by a 



consideration of certain species of Zoothamnium . . . 135 



b. Definition of Creation and Evolution : hypothetical histories 



of Zoothamnium in accordance with the two theories . 139 



c. The principles of Classification : natural and artificial 



classifications ... . .138 



d. The connection between ontogeny and phylogeny . .143 



V. PLANTS AND ANIMALS. 



a. Attempt to define the words plant and animal, and to place 



the previously considered types in one or other king- 

 dom ... . . 174 



b. Significance of the " third kingdom," Protista 180 



VI. SPERMATOGENESIS AND OOGENESIS. 



Origin of sperms and ova from primitive sex-cells : differences 



in structure and development of the sexual elements . 252 



VII. MATURATION AND IMPREGNATION. 



a. Formation of first and second polar ceils and of female 



pronucleus ... 257 



b. Entrance of sperm and formation of male pronucleus . . 258 



c. Conjugation of pronuclei . . 259 



