that the life cycle original for all metazoan phyla comprises 

 two phases, a pelagic larval and a benthic adult phase. This 

 then leads to extensive discussions, particularly of Haeckel's 

 "biogenetic law". 



The introductory chapter briefly discusses "primary larvae , 

 "adultation", direct development, and "secondary larvae". The 

 special section which follows occupies about three-quarters of 

 the book and systematically examines the marine larvae of all 

 metazoan phyla. The general section then discusses these data 

 in 10 short chapters, the last two being devoted to the evi- 

 dence for recapitulation in its modified and qualified sense. 



The book is well printed and illustrated with good, largely 

 original line drawings. 



121 . 



U.MITTWOCH. 1973. GENETICS OF SEX DIFFERENTIATION 



Academic Press, New York, etc. XIV,253pp., 40 figs., 6 tabs., 



author and subject indexes. $ 16.50 



Contents: 1. Classical genetics of sex differentiation; 2. 

 Genetics of continuous variation; 3. Aspects of the gene; 4. 

 Heterochromatin; 5. The nature of sex differentiation with 

 special reference to vertebrates; 6. Sex determination in man 

 and other mammals; 7. Genes, chromosomes, growth, and sex 



This interesting book elaborates a thesis based primarily on 

 recent findings of the author in mammals and birds. The thesis 

 and its wider biological implications become clear from a quo- 

 tation from the preface: 



The purpose of this book is to bring together evidence that 

 the sex chromosomes may affect the rates at which cells di- 

 vide and that the process of sex differentiation is based^on 

 differences in growth rates during development .... [It] is 

 hoped that the approach I have chosen - looking beyond the 

 formal gene-phenotype relationship and emphasizing^ the dynam- 

 ic relationship between chromosomes and growth - will lead 

 to a better understanding of the role of chromosomes in the 

 development of sexual and other characteristics, i.e., those 

 which are basically of a quantitative nature. 



Although it must be admitted that the direct evidence for 

 the thesis is still scarce, it is supported by much indirect 

 evidence, partly from outside the area of sex differentiation 

 itself, and this is expertly discussed in a series of concise 

 but well-organized chapters. The theory of sex determination 

 by Mendelian genes is dismissed, and much stress is placed on 

 the non-genic heterochromatic chromosome regions and their reg- 

 ulatory role in cell proliferation and growth generally, i.e. 

 in a variety of plants and animals and in both sexual and non- 

 sexual organs and phenomena. Thus the scope of the book is much 

 wider than the title indicates. 



Symposium reports 



122. 



B.I.CHERFAS, ed. 1972. GENETICS, SELECTION, AND HYBRIDIZATION 



OF FISH, translated from the Russian by R.Lavoott 



Israel Program for Scient. Translations, Jerusalem. VI, 269 pp., 



34 figs., 62 tabs. 



This volume contains 28 papers presented at a Conference held 

 in Leningrad in 1967. Although this is a long time ago, several 

 of the papers may still be of interest to fish embryologists , 



234 



