viii FOREWORD 



pleasure in reading these pages, or, at least, in looking at 

 the pictures. 



The difficulties which may be encountered by some Anglo- 

 Saxon readers may not necessarily result from inadequate 

 knowledge of their own language. They could be due in 

 part to the fact that the French author, owing to a certain 

 distrust of translations, has, despite his diffidence, written 

 this book directly in English. 



The author is indebted to his friends E. Faure-Fremiet 

 and Jacques Monod for helpful criticisms and discussions. 



Andre Lwoff 



Paris, France 

 January, 1950 



The author wishes also to thank the editors of the Archives 

 de zoologie experimentale et generate for kind permission to 

 reproduce Figs. 1 to 16, 19 (slightly modified) to 26, and 

 29. Figure 17 is taken from E. Chatton, A. and M. Lwoff, 

 and J. Monod, Compt, rend. soc. biol, 107 (1931); Fig. 18 

 from S. Villeneuve-Brachon, Arch. zool. exp. et gen., 82 

 (1940); Fig. 27 from E. Chatton, A. and M. Lwoff, and L. 

 Tellier, Coinpt. rend. soc. biol, 100 (1929) ; Fig. 28 (slightly 

 modified) from E. Faure-Fremiet, Bull. biol. France-Bel- 

 gique, 79 (1945); Fig. 30 from E. Chatton and J. Seguela, 

 Bull. biol. France-Belgique, 7 If. (1940); Fig. 31 from E. 

 Chatton and A. and M. Lwoff, Compt. rend. soc. biol., 107 

 (1931) ; and Fig. 32 from E. Faure-Fremiet and H. Mugard, 

 Compt. rend. acad. sci., 227 (1948). 



