NEW BIOLOGICAL BOOKS 



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 and the value of new books in the various fields of biology. In addition there will frequently 

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MORGAN ON ENTWICKLUNGS- 

 MECHANIK 



Being a review of Experimental Embryology 

 by Thomas Hunt Morgan. New York 

 (Columbia University Press) 192.7. 

 5! x 9$; xi + 7 66 - $7-5°- 



By S. K. Detwiler, Columbia University, and 

 H. B. Adelmann, Cornell University 



Embryology as a scientific discipline is 

 comparatively young. As a matter of 

 fact, it is just a century old, since it may 

 be said to have begun its modern epoch 

 in 1 8x8 with the publication of von 

 Baer's monumental work, Uber Entwickel- 

 ungsgeschichte der Thiere. Beobachtung und 

 Reflexion. The modern reader of this 

 classic can only marvel at its high level of 

 accuracy and the prophetic insight of its 

 author. 



For more than fifty years embryology 

 remained, almost of necessity, a purely 

 descriptive science, but with the publica- 

 tion of Wilhelm Roux's research concern- 

 ing the time of determination of the prin- 

 cipal axes of the frog embryo, Ueber die 

 Zeit der Bestimmung der Hauptrichtungen 

 des Froschembryo, in 1883, and his vigorous 

 advocacy of the experimental approach 

 to the solution of the problems of develop- 



ment, embryology may be said to have 

 entered upon a new era. 



This new "Zweig der Wissenschaft" 

 was termed by Roux developmental me- 

 chanics (^Entwickelungsmechanik') . Driesch 

 prefers to call it developmental physiology 

 (Entwickelungsphysiologiej, thus avoiding 

 a mechanistic implication, but in English 

 Experimental Embryology is the designa- 

 tion usually preferred. In the beginning 

 Entwickelungsmechanik met with many 

 obstacles, and its fond parent was fre- 

 quently called upon to justify its existence 

 and to shield it from attacks of the scorn- 

 ful. This he lost no opportunity to do. 

 Numerous programs of the work were 

 issued (1885, 1889, 1892., 1897, 1905, ctc.~) 

 outlining the field. He predicted a bril- 

 liant future for the child and it is only 

 just to say that his confidence has been 

 abundantly justified. 



As conceived by Roux, the goal of 

 Entwickelungsmechanik is a complete 

 causal analysis of every developmental 

 process. While recognizing that some 

 causal relationships might be deduced 

 from observation, Roux laid special stress 

 upon the value of experiments, of which he 

 recognized four principal types: (1) the 

 blind experiment (i.e., the I-wonder- 

 whether-something-interesting-might- 



419 



