396 



Scientific Proceedings (124). 



195 (1942) 



Rhythms in the rate of reproduction of Amceba bigemma. 



By E. FRANCES BOTSFORD (by invitation). 



[From the Osborn Zoological Laboratory, Yale University, New Haven, 



Conn.] 



A specimen of Amceba bigemma (Schaeffer) was isolated Decem- 

 ber 7, 192 1, and eight lines of its descendants have been bred in 

 pedigree cultures to the 100th generation (May 15, 1922). The cul- 

 tures have been carried on standard beef extract 1 and kept at a 

 temperature varying from 20 0 to 24 0 C. Vegetative division has 

 been uninterrupted by spore or gamete formation. The data ob- 

 tained by the daily isolation method show that the rate of division of 

 the organism under the conditions of the experiment fluctuates con- 

 siderably. At intervals during the pedigree there were daily divi- 

 sions, or frequently one division every other day for a short time. 

 Occasionally two fissions occurred in one day, while in a single 

 instance an Amceba divided three times during twenty-four hours. 

 Periods of inactivity when no fissions took place were common, 

 and varied in length from one to twelve days; but whereas the 

 absence of division for one or two days was of frequent occurrence, 

 that of over three days was rare. An average of the daily divi- 

 sions in eight lines for a period of ninety days showed the rate 

 to be slightly above one division in two days. 



In contrast to this daily irregularity there was a general period- 

 icity in the fission rate which was revealed only by an examination 

 of the data covering longer intervals of time. By averaging the 

 number of divisions in a single line for five-day periods, a rhythmic 

 character of the fission rate was apparent in the form of alterna- 

 ting periods of high and low reproductive activity; one low point 

 to the next comprising about twenty days. Whether these 

 rhythms are of the same nature as those in the Infusoria 1 can be 

 determined only after more study of this and other A mcebce in pedi- 

 gree cultures. 



'Woodruff and Baitsell, Journ. Exper. Zodlogy, 1911. Vol. IX. 



