94 PATTERNS AND PROBLEMS OF DEVELOPMENT 



parts, then shortens, and clear vesicles appear on its surface, first ante- 

 riorly, later elsewhere (Fig. 28, G, H). In neutral cyanide anterior shorten- 

 ing is followed by complete ectoplasmic cytolysis, progressing from the 

 anterior end posteriorly (Fig. 28, /), or in somewhat lower concentrations 

 bv ectoplasmic disintegration within the pellicle (Fig. 28, J). In death 

 from lack of oxygen anterior shortening is followed by appearance of clear 

 areas within, or clear vesicles on the surface, these changes also progressing 

 from the anterior end posteriorly (Fig. 28, K, L). In view of the findings 

 that cyanide does not greatly decrease oxygen uptake in Paramecium, 

 ectoplasmic differential susceptibility to this agent and to lack of oxygen 

 is of particular interest (see Appendix III, p. 736). The fact that the same 

 susceptibility gradient appears with both strong and weak acids and bases, 

 ultra-violet radiation, and lack of oxygen is also of interest, as indicating 

 that differential permeability is not the chief factor in determining the 

 gradient. An ectoplasmic gradient of osmophilic substance, decreasing 

 from the posterior region anteriorly, was found by Parke (1929) in P. 

 caudatum. The anterior vacuole of this species has a more rapid rhythm 

 than the posterior (Child and Deviney, 1926; Unger, 1926); but in P. 

 aurelia the posterior vacuole is more rapid, and in P. calkinsi the rate of 

 both is the same. These species differences in relative rate of vacuoles are 

 perhaps associated with difference in the gradient of the different species 

 and differences in form of body. Susceptibility and reduction gradients ap- 

 pear to be more strongly marked in P. caudatum than in P. aurelia, but in 

 general the posterior vacuole apparently receives fluid from a larger part of 

 the body than the anterior; this may be a factor in determining its higher 

 rate of contraction in some species. 



Other ciliates — Frontonia, Spirostomtim, Dileptus, and Woodruffia"^ — 

 show an anteroposterior ectoplasmic gradient of dye reduction. The gradi- 

 ent of Dileptus is particularly interesting; the whiplike, highly motile ecto- 

 plasmic organ at the anterior end reduces methylene blue much more 

 rapidly than the rest of the body, if not too deeply stained, and is also 

 much more susceptible than other parts to toxic action of dyes (Child, 

 1934&). Spirostomum is highly susceptible to dyes; but when slightly 

 stained with methylene blue, a slight reduction gradient appears; with 

 deeper staining this is reversed in direction in consequence of differential 

 injury by the dye. The susceptibility gradient in these forms parallels the 

 reduction gradient, except that in some individuals of Spirostomum a sec- 

 ond posteroanterior gradient appears in the posterior region. Spirostomum 



* Child, 19346, except unpublished data on Woodruffia. 



