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THE AMERICAN NATURALIST [Vol. XLVIII 



reactions. Intelligent behavior occurs in the lower 

 Arthropods. Even Paramecium shortens the time re- 

 quired to turn around in a tube, by repetition. Actions 

 formerly regarded as instinctive now appear to be mere 

 innate tendencies perfected by repetition. Thus the ideas 

 of fixity have essentially disappeared from this field. 



The response of organisms to injuries and the general 

 control of form in the lower groups has done much to 

 break down the ideas of fixity developed by Weismann 

 and embryological schools. Thus Child, the leading 

 American worker in this line, is able to control 

 size, form, number of eyes in the case of Planarians. 

 Various writers have found modifications inherited after 

 several generations of repeated stimulation (see Bateson, 

 M3). The development of anti-bodies (immunity) has 

 been shown to be a response occurring in connection with 

 many normal processes. The discovery of responses of 

 so many types has led to abandoning ideas of fixity even 

 among students of embryology and genetics. Thus we 

 note the recent decline of the doctrine of continuity and 

 independence of the germ plasm and kindred doctrines 

 and points of view, which constitute the central ideas of 

 fixity. It will accordingly he profitable to consider some 

 further facts which make the germ-plasm doctrine un- 



5. Aspects of the Untenability of the Germ 

 Plasm Doctrine 

 The presence of primordial germ plasm is assumed 

 even in sessile colonial organisms such as plants, ccelen- 

 terates, and in flatworms, etc., where under certain con- 

 ditions any small part of the body may give rise to a 

 complete organism. Here the theory is not needed to 

 explain the facts. 

 Child ('11) said: 



The theory of the continuity of the germ plasm as a sys 



