132 CM. Child. 



tlvlties in consequence of which morphological structure develops 

 Physical and chemical structure of protoplasm must not be con 

 fused with morphological structure : the distinction between the 

 two is important though often overlooked. As regards the indi- 

 vidual the former represents capacities for activity, i. e., for 

 transformation and transference of energy, or in short, functional 

 activity in the broadest sense. Form in the morphological sense, 

 is the combined result of this activity and the erxvironment, ex- 

 ternal or internal. According to this view, it is functional capacity 

 that is inherited rather than form : heredity is, strictly speaking, 

 a physiological and not a morphological problem. 



SUMMARY. 



1. Locomotion in Leptoplana is accomplished by two meth- 

 ods, swimming and creeping. In swimming the lateral regions 

 of the anterior part of the body perform undulating movements 

 in a dorso-ventral direction. Creeping movements are both ciliary 

 and muscular, the muscular movements consisting chiefly of an 

 alternate extension anteriorly or antero-laterally of the margins 

 of the head, adhesion to the substratum and muscular contrac- 

 tion, thus drawing the body forward. In creeping the margins 

 and posterior end of the body are used as organs of attachment. 



2. In consequence of the typical movements the tissues of 

 the body are subjected to typical mechanical tensions and pres- 

 sures which constitute formative factors. 



3. The effect of these mechanical conditions upon the tissues 

 is at least in part directly mechanical, but they may also act as 

 physiological stimuli to growth (formative stimuli). 



4. The effect of the mechanical conditions incident to locomo- 

 tion may be demonstrated experimentally by various methods. 

 The method described in this paper consists in making the pieces 

 of such a form that the direction of locomotion becomes curved 

 instead of straight. In these experiments the regenerating part 

 grows in the direction of the principal tension, even though this 

 form an angle of 90° with the typical direction of growth. 



5. The experiments lead to the conclusion that in Leptoplana 

 the regions of the body develop in a characteristic form because 

 they function or attempt to function in a characteristic manner. 



