STUDIES ON THE LIFE CYCLE OF PARAMECIUM. 30 1 



what he calls ' incipient fertilization "... would seem to bear 

 out this point, and to show that the number of generations, or the 

 period, over which a cycle extends, is not a point of great 

 moment." 



I have since found no reason to alter this opinion. But there 

 must be limits beyond which the " peculiar protoplasmic reac- 

 tions " of any individual do not extend, otherwise each would be 

 a law unto itself and there would be as many laws as individuals. 

 Certainly we may reasonably assume that there are limits of time, 

 and generations, which a "cycle" (if it exists) of any particular 

 species will not exceed. The earlier investigations apparently 

 indicated that about three months or about 100 generations was 

 the limit of the cycle of Paramecium. Calkins in his last paper 

 extended the cycle to about six months, or about 200 generations. 

 The present culture extends the "cycle" to more than twenty- 

 six months, and more than one thousand two hundred genera- 

 tions. The longest culture carried by Calkins (Culture A) lived 

 for twenty-three months, and attained 742 generations --but this 

 comprised four complete cycles, the last one terminating fatally. 

 It is necessary to contrast the cycle of Calkins' culture of about 

 six months duration, and two hundred generations, with the life 

 (cycle) of this culture, which is of twenty-six months duration at 

 present, and 1,238 generations. That is, this culture shows a 

 "cycle " twenty months longer in time, and, so far, of over one 

 thousand more generations. 



The character of the life history must also be taken into ac- 

 count. There is a marked difference in the character of the Para- 

 mecium curve after February, 1908, when the decidedly varied 

 environment was begun (cf. Figs. I and 2). A similar difference 

 in character is evident in the Gastrostyla culture when the more 

 constant medium was being maintained (cf. Fig. 5, July, August 

 and September), and the same is again strikingly shown in the 

 present culture of Paramecium in the experiments which sub- 

 jected the "same protoplasm " to a constant and a varied envi- 

 ronment simultaneously (cf. Fig. 4). 



The term cycle, as has been pointed out, is a relative one, but I 

 think it is necessary to extend the conception of the cycle (as 

 worked out on infusoria on constant media) to an unwarranted 



