MORPHOGENESIS 791 



membranelles differentiate, but a new mouth fails to develop and the 

 degenerative changes immediately appear. 



Fortner (1933) expressed the single, large macronucleus from the 

 body of gastrostyla-like hypotrichs (species?) by gently compressing the 

 organism between cover glass and slide. Such operations were followed 

 by a diminution in general mobility and contractile-vacuole pulse rate and 

 by the persistence of food vacuoles. Schwartz (1935) concluded that 

 amacronucleate pieces of Stentor coeruleus containing only micronuclei 

 are like totally anucleate specimens as to regenerative power, digestion, 

 and length of life. The amacronucleate pieces merely regulate external 

 form, without undergoing the sequence of changes involved in physiologi- 

 cal reorganization. 



In physiological regeneration following conjugation, autogamy, 

 endomixis, or analogous processes, the dimorphic nuclei have a common 

 origin from the synkaryon or from some micronucleus-like body, but 

 there is no convincing evidence that the micronuclei of strictly trophic 

 individuals are able to replace artificially removed macronuclei. It is 

 equally true that macronuclei do not give rise to new micronuclei. Numer- 

 ous attempts to create amicronucleate races operatively have not met 

 with success. The operated individuals survive no more than a few days 

 and do not regenerate new micronuclei. The origin of amicronucleate 

 races of Spathid'mm spat hula (Moody, 1912), Oxytrkha hymenostoma 

 (Dawson, 1919), O. jallax (Woodruff, 1921; M. E. Reynolds, 1932), 

 Paramecium caudatum (Lewin, 1910; Landis, 1920; Woodruff, 1921; 

 Schwartz, 1934), Didinium nasutum (Thon, 1905; Patten, 1921), 

 Urostyla grandis (Woodruff, 1921; Tittler, 1935), and possibly others, 

 appears to be the result of anomalous metagamic or post-endomictic dif- 

 ferentiation. 



Small fragments of the macronucleus of ciliates usually are able to 

 reconstitute the entire macronuclear system. In Stentor, for example, one 

 or two of the macronuclear nodules ultimately regenerate the long 

 moniliform chain. Schwartz (1935) thought that the process of re- 

 organization in this species serves to regulate the size relationships of 

 the different organelles. The surface relations of nucleus and cytoplasm 

 are adjusted by fusion, division, or deformation of the macronuclear 

 segments. 



As far as regeneration is concerned, the macronucleus appears to be 



