I04 C. M. Child. 



On the other hand the study of regeneration in the stricter 

 sense is not at all impossible under those conditions. The failure 

 of the new portion to attain full size is a minor matter. Indeed 

 the presence of food is a complicating factor in the study of reg- 

 ulation of lower forms, since it renders less possible the distinc- 

 tion between ordinary processes of growth and the regulative 

 processes. 



THE MOVEMENTS OF LEPTOPLANA. 



In Leptoplana, as in Stenostoma (Child, '02, '03a, '03b), 

 there is a close relation between form-regulation and movement. 

 A description of the characteristic methods of movement may 

 properly, therefore, precede the account of experiments. 



Locomotion in Leptoplana tremellaris is accomplished in two 

 ways, by swimming and by creeping. Lang ('84, pp. 634-636) 

 has described the movements of the polyclads and among them 

 those of Leptoplana. I desire, however, to consider these move- 

 ments with special regard to their mechanical effect upon the 

 tissues and for this purpose Lang's description does not suffice. 

 Figure I shows the outline and proportion of a specimen in fully 

 extended condition as when creeping. 



Swimming is accomplished by an undulating movement, dorso- 

 ventrally directed, proceeding posteriorly from the anterior end 

 of the lateral regions of the head and anterior portions of the 

 body, the median portions remaining meanwhile almost motion- 

 less. This method of swimming is called by Lang the flying 

 movement. In various other polyclads it appears in much more 

 extreme form than in Leptoplana and in some involves not only 

 the anterior regions but the whole lateral region of the body as 

 in Thysanozoon. 



It is interesting to note that in all cases where this undulating 

 movement extends over only a part of the lateral region of the 

 body, the region involved is the broadest portion of the body. 

 In Leptoplana it is not sharply marked off from other regions 

 posterior to it, as is the case in some forms, e. g., Stylochoplana 

 agiUs (Lang, '84, Fig. 2, Tafel II, also pp. 457 and 636). In 

 correspondence with the absence of sharp demarcation of the 

 undulating region in Leptoplana we find that the undulating 



