PHYSIOLOGICAL CHARACTERISTICS OF AXIATE PATTERNS iii 



tial reduction in the unpigmented Procotyla, a form without posterior 

 zooids, progresses from head to posterior end, except that the extreme pos- 

 terior tip may reduce somewhat more rapidly than levels slightly anterior 

 to it. The curves of Figure 32 indicate diagrammatically the differences in 

 the reduction gradients of Dugesia and Procotyla. They are intended 

 merely to show roughly the differences in rate of dye reduction, as indi- 

 cated by decoloration of methylene blue or change to red of Janus green 



Fig. 32. — Diagrammatic curves without quantitative significance, indicating differential 

 dye reduction in Dugesia dorotocephala {upper) and Procotyla flitviatilis Qoicer). A, anterior 

 end; F, level of fission;ordinates indicate degrees of decoloration or color change; abscissae, 

 body-levels. 



at a stage when reduction is about completed in the head region. In the 

 upper curve for D. dorotocephala the rate decreases from the head to the 

 fission zone, where it increases rather abruptly and remains high in the 

 posterior zooid region. The curve for Procotyla (below) indicates a con- 

 tinuous decrease in rate from anterior end posteriorly, except at the 

 posterior tip.^'^ 



'7 With slow staining, planarian ectoderm is rather susceptible to basic dyes; cytolysis 

 usually begins in the head region, while the body is only slightly or not visibly stained. With 

 relatively high concentrations (e.g., 1/20,000 Janus green, 1/5,000 or higher methylene blue) 

 and with rapid oxygen decrease during staining, it is possible to demonstrate the reduction 

 gradients on the ventral surface before cytolysis begins (Child, unpublished). 



