go PATTERNS AND PROBLEMS OF DEVELOPMENT 



PROTOZOA 



An ectoplasmic gradient has been demonstrated in many protozoa, 

 chiefly cihates, by differential reduction of methylene blue and differential 

 susceptibility to many chemical and physical agents, and the indophenol 

 blue reaction and reduction of permanganate have been used with a few 

 species. Results obtained with the different methods show a rather re- 

 markable agreement. 



In Amoeba susceptibility to cyanide decreases from tip to base of the 

 pseudopod (Hyman, 1917); and, according to Lynch (1919), animals in 

 the limax condition, that is, with a temporary anteroposterior axis, show 

 an anteroposterior gradient in the whole body. Bovie and Barr (1924) 

 have observed a similar gradient in susceptibility to radiation. Suscepti- 

 bility and permanganate reduction decrease from the mouth region basip- 

 etally in Noctiluca. Evidence of a longitudinal ectoplasmic gradient has 

 been obtained from all ciliates examined for the purpose — some thirty 

 species; but Paramecium has been more extensively studied than other 

 forms. With staining which is not appreciably toxic rate of reduction of 

 methylene blue in Paramecium ectoplasm decreases from the anterior end 

 posteriorly (Child, 1934&). In very low concentrations of oxidized dye 

 the ectoplasm of P. caudatum does not stain appreciably, but the ento- 

 plasm stains slowly, at least in the posterior region (Fig. 27, ^). In 

 slightly higher concentrations anterior ectoplasm does not stain, while the 

 posterior ectoplasm stains gradually and sooner or later shows toxic effect 

 with loss of structure, beginning at the posterior end and progressing ante- 

 riorly, and finally cytolysis progressing in the same direction (Fig. 27, 5). 

 These differential stainings occur when the dye solution is exposed to air. 

 They are not due to deeper staining of the posterior region in consequence 

 of entrance of dye through the mouth into the posterior entoplasm and 

 passage into the ectoplasm; the entoplasm may be uniformly stained 

 throughout, with ectoplasmic staining only in the posterior region. With 

 further increase of concentration, ectoplasm stains equally throughout; 

 and with decrease of oxygen, rate of dye reduction decreases from anterior 

 to posterior end (Fig. 27, C). Ectoplasmic reduction seems to occur a 

 little more rapidly about the oral region than in the general ectoplasm of 

 that body-level; this, however, is not entirely certain and is not indicated 

 in the figures. 



The facts suggest that some dye reduction occurs in the ectoplasm at 

 oxygen-levels in media exposed to air. If this is the case, it appears that 



