landscape, switching points, etc., - which previously were 

 expressed only in the unsophisticated language of biology -, 

 can be formulated more adequately in terms such as vector 

 fields, attractors, catastrophies and the like; going much 

 further than this, he develops many highly original ideas, 

 both strictly mathematical ones within the field of topology, 

 and applications of these to very many aspects of biology and 

 of other sciences. 



Thorn takes the standpoint (chapter 8) that geometrical or 

 field phenomena are a reality throughout living nature which is 

 brought to light by topology, and that we can describe such phe- 

 nomena and determine their formal properties and developmental 

 laws without asking, for the time being, what is their ultimate 

 nature (much as physicists use the gravitational laws with suc- 

 cess without yet having the remotest idea what gravity is). 

 Such a standpoint, if proved valid, would of course also have 

 far-reaching philosophical implications. 



As to the actual content of the book, we will restrict our- 

 selves to a few remarks. In chapter 9 the author applies his 

 topological concepts to gastrulation in amphibians, to the com- 

 parative gastrulation of vertebrates, to neurulation and dorsal 

 axis formation, to induction and individuation, and to some 

 problems of late morphogenesis. He comes up with topological 

 models for most of these processes which, he admits, are still 

 very speculative and subject to verification. In chapter 10 he 

 describes three classes of models for global organization of 

 metazoan organisms (static, metabolic, and hydraulic) and dis- 

 cusses organogenesis and cellular differentiation. In chapter 

 12 he successively discusses finality, the irreversibility of 

 differentiation, the origin of life, and evolution. 



In the reviewer's opinion (which is admittedly largely intu- 

 itive, due to a lack of suitable mathematical training) this 

 rich and important book may well on the long run initiate a 

 major revolution in biological thinking generally and in the 

 approach to morphogenesis in particular. 



6. 



G.D.WASSERMANN. 1972. MOLECULAR CONTROL OF CELL DIFFERENTIATION 

 AND MORPHOGENESIS, a systematic theory 



Marcel Dekker, New York. Quantitative Approach to Life Science 

 Vol.2. XVI, 582 pp., 5^ figs., 4 tabs., author and subject in- 

 dexes. $ 36.50, £ 17.35 



The author of this intriguing monograph is a physicist with a 

 thorough knowledge of molecular biology and biophysics. The 

 book is concerned with the basic and topical question whether 

 cell differentiation and morphogenesis can be explained entire- 

 ly on the basis of the specific properties of individual cells 

 as determined by their biochemical activities, or whether it is 

 necessary to invoke less specific global or supracellular prin- 

 ciples (e.g. fields or gradients). The author is a confirmed 

 proponent of the former view, and here presents a theory which 

 is intended to bridge the gap between genetics and embryology 

 directly via molecular biology. The theory is best characterized 

 as a molecular automaton theory. Because of its extreme complex- 

 ity it is impossible to give a complete review here; instead, we 

 restrict ourselves to highlighting some of its salient features. 



The book is entirely hypothetical in character, and the author 

 concedes that this theory is supported by indirect evidence only. 

 The central chapters of the book will make tough reading for most, 



185 



