Chapter 4 



GERMINAL ORGANIZATION AND 

 INDUCTION PHENOMENA' 



Albert M. Dalcq 



To the Memory of my son Andre [ig26-ig^8] 



In this volume whose purpose it is to discuss the multiple aspects of growth, a study 

 of germinal organization is a prerequisite, especially if it examines the constituents 

 involved and their spatial and dynamic relations. At definite moments in develop- 

 ment, these relations, granted a favorable milieu, allow growth to occur and 

 flovirish to various extents, and insure the prosperity and resistance of the 

 organism, while their deficiency sometimes causes its more or less tragic dis- 

 organization. 



According to current ideas, growth makes its appearance only when the 

 various types of cells have been formed by cytodifTerentiation or histodiflferen- 

 tiation, but this is probably too radical a distinction. In development, a clearcut 

 division into periods devoted to distinct tasks does not exist; in spite of most 

 textbook presentations, growth, the most imperious urge of living beings, begins 

 insidiously at early stages. Moreover, the production of eggs and spermatozoa 

 results from intense growth processes. It is the characteristic feature of sexual 

 reproduction that growth in both kinds of gametes enters a sort of blind alley if 

 fertilization does not take place. Male gametes, so far as is known, are never able 

 to develop by themselves, and female ones do it only exceptionnally; partheno- 

 genesis is always either secondarily acquired or experimentally achieved. In most 

 cases, the inertia of the egg makes fertilization necessary for the release of the 

 new life cycle. 



Our task is here to examine the main data necessary for comprehension of the 

 general conditions reigning in a young organism until the moment when growth 

 becomes conspicuous. This means that we should consider gametogenesis and 

 early development as processes which gradually build up the organized whole, 

 and that we should analyse the special features progressively acquired by the cells 

 composing first the presumptive areas, and later the germ layers, and the several 

 blastemas. To understand the fate of these primordia, induction phenomena 



^ I would like to express my thanks to Miss Martha Brice, Fulbright student in my 

 Laboratory, for the linguistic revision of this manuscript. Mr. Karl Enselberg, Univ. oi 

 Pennsylvania, also diligently helped me to include, in 1958, several recent results. 



Literature p. 483 



