Studies on Regulation. IV. 97 



Is not a favorable form for exact measurement. It was necessary 

 to repeat all measurements several times In order to be certain 

 that they were approximately correct. In all cases the attempt 

 was made to secure the measurements while the animal was In 

 the fully extended condition. In order to accomplish this It was 

 often necessary to stimulate the specimens to movement and then 

 to measure them while moving. A small millimeter scale which 

 could be immersed In the water was used for whole animals and 

 the longer pieces, while the smaller pieces were measured under a 

 low power of the microscope with the aid of an ocular micrometer. 

 In all cases the measurements were reduced to millimeters. 



The measurements which were commonly made are as follows : 

 length of whole body, distance from anterior end of head to 

 middle of group of eyes, distance from anterior end of head to 

 anterior end of pharynx, length of pharynx, width of head in 

 region of the eyes — In whole animals this is usually the widest 

 part of the body, but In short pieces undergoing regulative changes 

 of form, the widest part Is anterior to the eyes; in such cases meas- 

 urement both of the widest part and the eye-region was made — and 

 finally the width of the body at the posterior end of the pharynx. 

 In regenerating pieces with new tissue the dimensions of the new 

 tissue and the position of regenerating pharynx and genital ducts, 

 If present, were also carefully determined by measurement. Since 

 a cut surface undergoes marked contraction In Leptoplana and 

 the new tissue arising from It consequently occupies only a part 

 of the area of the original cut surface it was necessary In many 

 cases to determine with great care the width of the body just 

 anterior to the cut, the width of the new tissue at its origin, the 

 difference of these measurements representing the degree of con- 

 traction of the cut surface. Measurements of pieces without ce- 

 phalic ganglia are not strictly comparable with those of pieces 

 In which the ganglia are present, since the former rarely extend 

 fully. It will not be necessary in most cases to give all these meas- 

 urements in detail since the figures, which are drawn from them 

 in almost every case, will show the changes with sufficient clear- 

 ness. 



