No. 500] LIFE CYCLE OF PARAMECIUM 521 



a constant culture medium of hay infusion which is 

 essential to the continued life of the organism, and that 

 depression effects which appear more or less regularly 

 are due, in part, to a process of slow starvation— rather 

 than to a loss of the power of assimilation. Recovery 

 from these periods is effected by various stimuli (beef 

 extract, etc.), because the lacking factor, or factors, is 

 thereby supplied. Calkins himself points out the marked 

 similarity of the morphological changes which he obtained 

 in the earlier cycles of his Paramecium cultures with those 

 found by Wallengren 4 to occur in Paramecia which had 

 been intentionally starved. I have also called attention 

 to this similarity in discussing the life cycle of various 

 hypotrichous infusoria and have suggested that the effect 

 of such stimuli as beef extract, etc., may be essentially 

 that of concentrated nutrition." 



In connection with some experiments on the effect of 

 various stimuli on the life cycle of infusoria, 6 I have had 

 occasion to carry a culture of Paramecium for over a 

 year and the data derived from this work are believed to 

 throw some light on the effect of a varied environment on 



On May 1, 1907, a "wild" Paramecium was isolated 

 from a laboratory aquarium and placed on a depression 

 slide in five drops of hay infusion. When this animal 

 had divided twice, the four resulting individuals were 

 isolated on separate slides, and in this manner were 

 started the four lines, I-a, I-b, I-c and I-d, which compose 

 this culture. 7 The culture has been continued by the 

 isolation of an individual from each of these lines almost 

 daily throughout the life of the culture up to the present 

 time (May 6, 1908) and a record has been kept of the 



* Wallengren, H. Inanitionserscheinungen der Zelle. Zeit. f. allg. 

 PhilsiohHlir, I, 1, 1901. 



• Woodruff, L. L. An Experimental Study on the Life History of Hypo- 



^'^WoodrurT" ^ L Effects of Alcohol on the Life Cycle of Infusoria. 

 Biol. Bull, XV, 2, 1908. 



T Further details in regard to the technique are given in previous papers. 



