PLATES 



I A live fertilized mouse egg, showing the whole sperma- 

 tozoon in the cytoplasm. Photograph by J. Smiles. 



frontispiece 



II Fertilization of the egg of Urechis caupo. Tyler (1932). 



facing page 18 



III Agglutination of a 2% suspension of spermatozoa of 



Megathtira cremdata in the presence of homologous 



egg water. Tyler (19406). 22 



IV Dissolution of egg membrane of Megathura crenulata 



by an extract of a i % homologous sperm suspension. 

 Photograph by A. Tyler. 36 



V The two sorts of flower of Forsythia X intermedia. 



Photograph by Royal Botanic Gardens, Kew. 52 



IX 



