CHANGE OF SHAPE IN PLANARIA. 2Q5 



or a decrease or a modification in kind according to the character 

 of the factor inducing the change. The change in shape in the 

 pieces of P/anaria, etc., does not in itself involve any such change 

 in functional capacity, moreover, functional adaptations to me- 

 chanical tension and pressure consist, usually if not always, in an 

 altered resistance to the mechanical factor, not in a change of 

 shape which accords with the laws of mechanics. The change 

 in shape in these turbellaria is essentially similar to what would 

 occur under the same conditions in any material of similar phys- 

 ical constitution and there is not the slightest evidence that it 

 results from a change in functional capacity. 



There is little doubt, however, that functional adaptations 

 result from the change of shape : as was suggested above, it is 

 probable that the cessation of the change and the final attain- 

 ment of a more or less characteristic shape, i. e., a condition of 

 equilibrium, is in part the consequence of the functional reaction 

 of the differentiating and redifferentiating tissues to the altered 

 mechanical conditions. In other words, the change of shape 

 brings about the functional adaptation instead of resulting from it. 



But even though these changes in shape do not appear to be 

 functional adaptations in Driesch's sense, they are functional 

 regulations in my sense, and probably the simplest possible kind 



of functional regulation. 



HULL ZOOLOGICAL LABORATORY, 

 UNIVERSITY OF CHICAGO, 

 March, 1909. 



BIBLIOGRAPHY. 

 Child, C. M. 



'02 Studies on Regulation. I., Fission and Regulation in Stenostoma. Arch. 



f. Entwickelungsmech., Bd. XV., H. 2 and 3, 1902. 

 '03 Studies, etc. II., Experimental Control of Form- Regulation in Zoolds and 



Pieces of Stenostoma. Arch. f. Entwickelungsmech., Bd. XV., H. 4, 



1903. 

 'o4a Studies, etc. IV., Some Experimental Modifications of Form-Regulation 



in Leptoplana. Journ. Exp. Zool., Vol. I., No. i, 1904. 

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Vol. I., No. 3, 1904. 

 '040 Studies, etc. VI., The Relation, etc. Anterior and Lateral Regeneration. 



Journ. Exp. Zool., Vol. I., No. 4, 1904. 



Studies, etc. VII., Further Experiments on Form-Regulation in Lepto- 

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