

NEW BIOLOGICAL BOOKS 



4*-5 



that while such phrases as polarity, 

 symmetry, organ-forming germ regions, 

 morphogenetic processes and differential 

 cleavages may be useful when used in a 

 descriptive sense, they become deceptive 

 when employed as if something were 

 explained by them. We are, after all, far 

 from understanding the essential nature of 

 symmetry. At present we may only 

 describe it as it is normally manifested 

 with its experimental alterations. Its 

 cause we may never understand. It is, as 

 Bateson suggested, essentially organismic 

 pattern and may very likely have its basis 

 in protoplasmic or molecular pattern. 



For Professor Morgan, then, develop- 

 ment would consist largely in the nuclear 

 domination of the cytoplasm, which is 

 responsive on the one hand to the nucleus 

 and on the other to its external and 

 internal environment. 



One of the most interesting sections of 

 the book is that dealing with the mutual 

 interactions of the embryonic organs upon 

 one another. Herbst deserves the credit 

 for having first in 1901 clearly emphasized 

 the importance of this field. In his 

 Formative Rei%e in der thierischen Ontogenese 

 he listed and discussed a number of ex- 

 amples of external and internal formative 

 stimuli in ontogeny. This aspect of 

 development was for many years more or 

 Jess neglected and it is only within recent 

 years that the work of Spemann and his 

 students has again focused attention upon 

 it. The fact that a neural tube or even an 

 eye can be induced to form from belly 

 ectoderm by an underlying implant of the 

 roof of the archenteron or a piece of 

 neural plate, or that a more or less per- 

 fectly organized embryo can be induced to 

 form by implanting the dorsal lip of the 

 blastopore, has revealed again in a most 

 striking manner the mutual influence of 

 embryonic parts and makes us suspect 

 that there are undoubtedly others just as 



important of which we are unaware. 

 Whether Spemann's conception of an 

 "Organi%ator" controlling the differentia- 

 tion of the embryo will stand is, perhaps, 

 doubtful. The experiment, as Professor 

 Morgan points out, may, at any rate, be 

 interpreted as proving that "the forma- 

 tion of the neural plate depends on the 

 presence beneath it of chorda-mesoderm 

 and that the ectoderm of the upper hemi- 

 sphere is totipotent in its responsiveness 

 to this material." 



As regards the subject of artificial 

 parthenogenesis, a very complete summary 

 of the work is given. The interpretation 

 of results in this as in many other fields is 

 still unsatisfactory. "The fact that un- 

 fertilized eggs may be induced to develop 

 into normal embryos by artificial agents of 

 the most diverse kind, rather than the 

 hypotheses to account for the change, is 

 the outstanding feature of all this work" 

 (p. 581). 



Professor Morgan is hopeful that ulti- 

 mately we shall find a physical, chemical 

 or physico-chemical explanation of all 

 developmental phenomena. It is entirely 

 possible that one day we shall understand 

 fully the chemical and physical aspects of 

 fertilization, cleavage, gastrulation and 

 differentiation, but there would still re- 

 main to be explained the configuration of 

 physical and chemical processes that is 

 characteristic of the development of each 

 organism. As Professor Kingsbury has 

 put it 



Life in an organism today is like a tapestry in 

 which the threads of warp and woof are woven into 

 a pattern of exceeding intricacy and delicacy whose 

 weaving has been going on since the beginnings of 

 life. You may analyze the threads of process as they 

 run in and out today in terms of chemistry and 

 physics but the pattern stands as a history of the past 

 and the weaving is still largely a secret of the ages. 



The pattern of the genes may be cited as 

 an example. We may describe the con- 



