io8 PATTERNS AND PROBLEMS OF DEVELOPMENT 



As regards gradient pattern and its changes, it will perhaps appear more 

 clearly in following chapters that there is considerable similarity between 

 this functional pattern and physiological patterns of development. 



Transplantation and reconstitution of pieces of Mnemiopsis give evi- 

 dence of a persistent polarity but not of a gradient in time of reconstitu- 

 tion in pieces from different body-levels/-^ 



TURBELLARIA 

 PLANARIANS 



Because of their capacity for reconstitutional development, planarians 

 have been extensively used by many investigators as material for various 

 lines of experiment. The relation of reconstitutional pattern to body-level 

 of origin of the piece, as described in chapter ii, indicates that axiate pat- 

 tern of the parent body plays an essential part in determining the pattern 

 of reconstitution in the isolated piece. How far this is true will appear 

 more clearly in following chapters. Assuming that it is true, it is obvious 

 that information concerning the physiological characteristics of planarian 

 axiate pattern may be expected to aid in analysis of reconstitution and 

 perhaps of other forms of development. 



Determinations of oxygen uptake in pieces from different body-levels 

 of Dugesia dorotocephala by the Winkler method, with due care to elimi- 

 nate, as far as possible, sources of error and complicating factors, give 

 definite and consistent results.^^ Determinations on pieces of different 

 lengths at different periods after section showed that, following section, 

 rate of respiration of planarian bodies cut into short pieces (i/8) is much 

 higher than when cut into longer pieces (1/3) and that the longer pieces 

 show only a slightly higher rate than bodies with only head and posterior 

 end removed. Averages from the determinations in Hyman's Table i are: 

 for bodies with head and posterior end removed, 1.40 cc. of oxygen per 



'3 Coonfield, 1936a, b, 1937a, b; Coonfield and Goldin, 1937. 



'^ Hyman, 1923&. Since an earlier study of the effect of feeding and starvation on the 

 respiration of this species (Hyman, 19196) had shown that a marked increase in oxygen uptake 

 occurs on feeding, and that, in absence of food, oxygen uptake decreases in about a week to a 

 level which remains almost constant for some weeks following, and since size of the digestive 

 tract differs at different levels, the animals for determination were kept without food 6-18 

 days in order to eliminate, as far as possible, effects on total respiration of differences in 

 activity in different parts of the digestive tract. Animals of the same length, from one stock and 

 without sex organs, and pieces as nearly as possible the same length were used in all lots to 

 be compared. In all determinations head and posterior end were removed so that a cut sur- 

 face was present at each end of each piece. Each determination was repeated on from seven 

 to eleven different lots of material. See Appendix I (p. 729). 



