STUDIES ON THE LIFE HISTORY OF PROTOZOA. 



IV. DEATH OF THE A SERIES. 



CONCLUSIONS. 



BY 



GARY N. CALKINS. 

 With 3 Plates and 3 Figures in the Text. 



Experiments on the life-history of Paramcecium caudatum have 

 now been carried on continuously for 29 months. Two series, 

 designated as the "A series" and the "B series," were started on 

 the first of February, 1901, with individuals from different 

 sources. The B series died out in May, 1902, in the 570th genera- 

 tion; the A series on December 19, 1902, in the 742d genera- 

 tion. A third series — "C" was started in June, 1902, with an 

 individual from Cambridge, Mass., and died out in June, 1903, in 

 the 379th generation. The progress of the first two series has 

 been recorded from time to time,^ and in the present paper I 

 wish to give the history of the last cycle of the A series and to 

 consider the results in relation to some general biological prob- 

 lems and theories. 



I. THE JUNE AND DECEMBER (19O2) PERIODS OF DEPRESSION. 



As described in the earlier Studies (I and III) the general 

 vitality of the two series, A and B, as expressed by the daily 

 division rate, underwent periodic cycles of vigor and depression. 



^(1) Studies on the Life History of Protozoa. I. The Life Cycle of Paramcecium 

 caudatum. Archiv. f. Entwk. XV, 1, 1902. 



(2) Studies, etc. II. The Effect of Stimuli on the Life Cycle of Paramcecium 

 caudatum. (With C. C. Lieb). Arch. f. Protistenkunde. I, 1, 1902. 



(3) Studies, etc. III. The 620th Generation of Param. caud. Biol. Bull. Ill, 5, 

 1902. 



