AMICRONUCLEATE RACES OF INFUSORIA 335 



PARAMECIUM CAUDATUIVI 



During January, 1920, the author's course in protozoology 

 made a study of the cytology of Paramecium aurelia and Para- 

 mecium caudatum and incidentally discovered a race which 

 had the usual characteristics of P. caudatum except that no 

 micronucleus could be demonstrated. It seems justifiable to 

 conclude that a micronucleus was absent, though the race was 

 not studied for a long period in pedigree culture. Apparently 

 it was a race comparable to that recently discovered by Landis. 



DISCUSSION 



The facts in regard to amicronucleate races of ciliates are as 

 yet too few to warrant an attempt to discuss from in a com- 

 prehensive way the questions which they present, though a brief 

 survey and interpretation will serve to delineate the problem. 



Confining attention to free-living ciliates, we find five 

 species in which amicronucleate races have been definitely an- 

 nounced, viz., Oxytricha hymenostoma (Dawson), Oxytricha 

 fallax (Woodruff), Urostyla grandis (Woodruff), Paramecium 

 caudatum (Landis, Woodruff), and Didinium nasutum (Patten). 

 To extend the survey to the general literature on the mor- 

 phology of ciliates is not fruitful, because, unless the micro- 

 nucleus was the special point of study, the evidence is of 

 little value. Two records, however, may be mentioned which 

 are highly significant. Thon, in 1905," made a careful cytolog- 

 ical study of Didinium, but was unable to discover a micronu- 

 cleus, and Miss Moody, in 1912,^ carried on a long pedigree 

 culture of Spathidium spathula which revealed no micronuclei. 

 It is difficult to conceive that either of these authors could have 

 overlooked micronuclei if present. The micronuclei of Didinium, 

 though small, are usually fairly easy to demonstrate when present. 

 The micronuclei of Spathidium were clearly observed by Maupas,^ 



^ K. Thon, Ueber den feineren Ban von Didiniiun nasutum. Archiv f. Pro- 

 tistenk., 1905, Bd. 5, S. 282. 



' J. E. Moody, Observations on the life-history of two rare ciliates, Spathidium 

 spathula and Actinobolus radians. Jour. Morph., 1912, vol. 23, p. 349. 



^ E. Maupas, Sur la multiplication des Infusoires cilies. Arch. d. Zool. Exper. 

 et Gener., 1888, 2" Serie, T. (j, p. 247. 



