730 PATTERNS AND PROBLEMS OF DEVELOPMENT 



tions, a question raised in connection with other work, with this method, Allee and 

 Oesting (1934) have shown that Hyman's data on planarian pieces from different 

 body-levels are not open to criticism. A recent comparison of the Winkler method 

 with respirometer and Van Slyke methods has shown the Winkler method to be as ac- 

 curate as the others (J. Wilder, 1937)- 



As a matter of fact, except for determinations with very small amounts of material, 

 the Winkler method has certain very definite advantages over most respirometer meth- 

 ods, particularly with aquatic material easily excited to movement. The material is 

 in normal environment and entirely undisturbed during the respiratory period, and 

 motor activity is reduced to a minimum. With most respirometer methods the shak- 

 ing and the starting and stopping tend to induce movement; and even if they do not 

 induce visible movement, their effects on respiration are not known. 



The assertion, unsupported by proof, was also made by Shearer (1930) that the 

 differences in oxygen consumption found by Hyman in planarian pieces are too small 

 to be significant; that they are statistically significant was shown by Hyman (1932(7). 

 The high degree of consistency of Hyman's data on pieces from different levels, on 

 age differences, on effects of feeding and starvation, and on reconstitution in Dugesia 

 with repeated determinations constitutes strong evidence that they represent real 

 respiratory differences. Before they can be discarded, equally consistent and con- 

 clusive evidence must be presented to show that they are incorrect. Moreover, it is 

 also of some interest to note that these differences in oxygen consumption are closely 

 paralleled by differences in susceptibility to cyanide, and the differences at different 

 body -levels, by dye-reduction gradients. 



Averages of determinations of oxygen consumption by a respirometer method made 

 by Shearer (1930) on two planarian species show a respiratory gradient; but, because 

 of the great variations and because of observation of greater motor activity in anterior 

 than in posterior pieces, the author holds the opinion that the respiratory gradient 

 observed results from the differences in motor activity. Apparently he made no 

 attempt to decrease motor activity, though it is possible, at least with most planarian 

 species, to eliminate it almost entirely by using short pieces instead of large fractions 

 of the body length. There is no evidence in his paper that the question whether a 

 temporary increase of respiration followed section was considered, nor are there any 

 data concerning the effect on respiration at different body-levels of presence or absence 

 of food and digestive activity in the gut; it is not stated whether the heads of the an- 

 terior pieces were removed; motor activity is greater when the head is present. The 

 data are not given in full but only as averages with a few of the determinations to 

 show the variation. Determinations for the two species are not given separately, 

 although the forms which he calls ''Planaria nigra" and "P. ladea" (incorrectly) sup- 

 posedly belong to different families and genera. The possibility that the great varia- 

 tion found may be due to the method and lack of proper precautions is not considered; 

 and because of this variation, the consistency and uniformity of Hyman's data are 

 criticized. He is apparently also ignorant of the fact that both Hyman and Parker 

 used species with a posterior zooid {D. dorotocephda and D. tigrina), while the forms 

 which he used, if they can be properly identified, have no such zooid. The posterior 

 zooid has a respiration about as high as that of anterior regions of the anterior zooid. 

 Concerning determinations made on Thysanozoon, a polyclad, Shearer (p. 263) 



