628 PATTERNS AND PROBLEMS OF DEVELOPMENT 



new patterns but are reconstitutions from portions of the parent pattern 

 or in certain orientation with respect to it. In the longitudinal fissions of 

 flagellates the spirals and asymmetries are apparently remade in relation 

 to a polar pattern. Divisions of the two species of Spirotrichonympha, as 

 described by Cleveland, provide interesting evidence on this point (see 

 p. 617). In S. polygyra the four spiral bands unwind, two of them form 

 a new spiral about each new polar axis, and two new bands develop about 

 each axis. In S. hispira a new band begins to develop in the parental an- 

 terior region, migrates posteriorly, and becomes spiral only after it reaches 

 the original posterior end, which becomes a new anterior end. Moreover, 

 when the spirals appear, they are at first irregular and only gradually 

 attain the regularity characteristic of the fully developed animal. Cleve- 

 land's description suggests that the new spiral patterns are determined 

 by a more general longitudinal pattern already present in the new an- 

 terior regions. When Stcntor divides, the new peristomial band is not at 

 first spiral and only gradually attains its definitive form, apparently in 

 relation to an axiate pattern already present. According to a personal 

 communication from Dr. C. V. Taylor, the ciliate Colpoda duodenaria 

 at the beginning of excystment is almost completely radial, as far as 

 visible pattern is concerned. The ends of the ciliary meridians center 

 about the two poles with only slight indication of the spiral asymmetry 

 characteristic of the fully differentiated individual. The oral region be- 

 gins development as a shallow invagination near, and at one side of, the 

 anterior pole and progresses posteriorly in a slight spiral. In association 

 with this spiral invagination of the mouth the anterior portions of the 

 ciliary meridians undergo spiral twisting As the oral region migrates pos- 

 teriorly, the anterior polar region changes its position correspondingly, 

 with flexure of the polar axis, so that the original anterior pole comes 

 eventually to lie somewhat anterior to the mouth, but distinctly lateral 

 as regards the whole body. At the posterior end, however, the radial 

 arrangement of the ciliary meridians persists. Spiral pattern in this species 

 is apparently almost completely obliterated in the encysted stage and 

 reconstitutes in relation to a polar pattern on excystment. 



Division in many forms, both flagellates and ciliates, involves what 

 seems to be more or less dedifferentiation of parental organs and develop- 

 ment of new organs, either in normal relation to each other or, in case of 

 the cirri of hypotrichs, in localized areas with a following change in posi- 

 tion, apparently in relation to a pattern. 



In short, various lines of evidence indicate that in the protozoa, as 



