In the first part on plasmatic maturation of the egg, he comes to the conclu- 

 sion that there is a causal sequence in plasmatic and nuclear maturation. The 

 spatial distribution of the plasmatic inclusions is based upon the structure of the 

 "groundplasm". The inclusions have no organ-genetic significance, but can be 

 necessary for the normal development of certain organ-systems. 



From the second part on determination the author concludes that the prin- 

 ciple of progressive determination does not hold for the cleavage period up 

 to the blastula stage. Determination is not based upon a special segregation of 

 organ-forming substances, but must depend upon the structure of the ground- 

 plasm which is also the seat of the power of regulation. The local properties of 

 the ground plasm determine the differentiation of the enclosed nucleus. The role 

 of cleavage is thought to be the provision of totipotent nuclei in the various 

 plasm areas and the spatial segregation of these groundplasm areas. 



The third part deals with the various gradient theories and the phenomena 

 of induction and organization. The author finds many points of correspon- 

 dence with the conclusions made in Child's book "Patterns and problems of 

 development", 1941. He however denies that gradients are based upon dif- 

 ferences in metabolic activity, but states that the latter are merely an expres- 

 sion of processes of differentiation. 



In the last part the relation between the genes and the plasm gradients is 

 discussed. The author concludes that gradients actually exist and play a decis- 

 ive role in the process of differentiation. Their nature and origin remain how- 

 ever questionable. He denies the role of substances as well as metabolic grad- 

 ients, but concludes that differentiation must be based upon gradients in the 

 structure of the groundplasm. Direct evidence is however still restricted. 



So far the author's considerations are very well argued. His further sug- 

 gestion that chromosomes also possess gradients, and that genes of a certain 

 chromosome gradient traject can only react with a certain plasm gradient 

 traject is still too speculative, and reduces to some extent the great value of 

 this important work. 



This very interesting theoretical work deals with a large number of fund- 

 amental problems, in which, we hope, all embryologists will be interested, so 

 that this work will contribute to a sharper theoretical planning of the experi- 

 mental analysis and consideration of the results obtained, which is a highly 

 desirable aspect. The fact that the work has been written in war time, and 

 had to wait so long before publication could be prepared, has led unfortunately 

 to the fact that several recent advances in the experimental analysis have not 

 been incorporated and synthesized in this work. 



P. D. NIEUWKOOP 



"MITOSE, 



die Bewegung der Chromosomen bei der Zellteilung" 

 1954 



by Fr. Schrader Verlag Franz Deuticke, Wien 



150 pp. with 19 figs Price: ? 



Since 1944 so much progress has been made in the analysis of the process 

 of mitosis, changing our opinions, that a revision of the first edition has become 

 highly desirable. Particularly the use of the phase contrast microscope and the 

 polarisation microscope, and the development of new techniques for the electron 



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