no PATTERNS AND PROBLEMS OF DEVELOPMENT 



allowed to run 15-24 hours, and the oxygen uptake was calculated per 

 gram per 24 hours. In all ten lots anterior halves of the anterior zooid 

 consumed more oxygen than posterior halves; and posterior zooid pieces, 

 about the same as the anterior pieces. Susceptibility to cyanide gives sim- 

 ilar results.^^ 



Colorimetric estimations of CO, production on pieces of D. doroto- 

 cephala gave results essentially similar to those of Hyman as regards in- 

 crease of respiration following section in shorter pieces and presence of a 

 gradient in the anterior zooid (Robbins and Child, 1920). From colori- 

 metric CO2 determinations on pieces of D. tigrina Parker (1929) concluded 

 that this species shows no evidence of a gradient; but, as a matter of fact, 

 his data agree with and confirm those of Hyman and Robbins and Child."' 



Because of their pigmentation and susceptibility to basic dyes, most 

 planarian species are not favorable material for observation of dye reduc- 

 tion; but reduction can be followed readily on the unpigmented, or only 

 slightly pigmented, ventral surface of a number of pigmented species. In 

 D. dorotocephala dye reduction (Janus green) occurs most rapidly, and at 

 about the same time, anteriorly and in the posterior zooid region and pro- 

 gresses posteriorly in the anterior zooid, the last region to reduce being 

 postoral, just anterior to the fission zone. In animals long enough to have 

 a second posterior zooid the posterior part of the posterior zooid region 

 may show slightly more rapid reduction than its anterior part. Differen- 



'5 Dr. R. M. Fraps permits mention of unpublished data obtained with a respirometer de 

 vised by him (Fraps, 1930) possessing certain advantages for this type of experiment. These 

 data confirm Hyman's determinations as regards difference of respiratory rate at different 

 body- levels in Dugesia. 



'^ Parker finds no definite difference in anterior and posterior halves. None is to be expected, 

 because this species, like D. dorotocephala , has a posterior zooid region with a higher respiration 

 than the posterior part of the anterior zooid. Table 5 shows that a piece from the anterior re- 

 gion has about the same oxygen uptake as one of equal length from the posterior zooid. In 

 another series of experiments, using the second to the fifth i /6 pieces, anterior and posterior 

 sixths being discarded, the average rates of CO^ production in milligrams per gram per 

 minute are: second 1/6, 0.00721; third, 0.00694; fourth, 0.00702; fifth, 0.0071 1. Second and 

 third pieces are in the anterior zooid, and COj production is less in the third than in the second; 

 the fourth sixth includes a part of the second zooid, and its CO, production is consequently 

 higher than that of the third. The fifth piece is wholly in the posterior zooid region, perhaps 

 even in a third zooid (see pp. 41, 321) and has a still higher CO2 production. These results are 

 exactly according to expectation on the basis of the other data on respiration and data on 

 head frequency and susceptibility to cyanide. The only question is whether the differences of 

 Parker's data are large enough to be significant. Whether the animals used in these experi- 

 ments were sexually mature is not known. The presence of the genital cloacal complex posterior 

 to the mouth may increase the respiration of this region over that in asexual animals. Deter- 

 minations of oxygen uptake of planarians by Shearer are discussed in .\ppendix 1 (p. 730). 



