500 JENNINGS— HEREDITY IN PROTOZOA. [April 24, 



have been able to isolate, not merely two permanently differentiated 

 lines, but eight. Of course, it would require merely more extensive 

 and intensive work to isolate others ; doubtless the number to be 

 isolated would depend only on the accuracy of the methods used. 



To my great regret, I was unable to take the steps necessary to 

 determine the number of micronuclei in the various pure lines with 

 which I worked. The animals multiply so rapidly that with several 

 lines in progress it is quite impossible even to keep up with the data 

 for size alone; probably half my experiments were lost on this 

 account, after much work had been spent on them. It was then out 

 of the question to carry on at the same time the staining processes 

 necessary to determine with certainty the number of micronuclei. 

 For work of the kind presented in this paper, a syndicate of investi- 

 gators is needed for keeping track of the various important aspects 

 of the matter. In the case of two of my lines the number of micro- 

 nuclei was determined; D (larger) had one; c (smaller) had two. 



I may be permitted to add to the precise data thus far given a 

 personal impression or surmise. Though, as I have shown, inter- 

 mediate lines occur, I believe it will be found that most Paramecin 

 can be placed in one of the two groups that we have called "can- 

 datum" and " aiirelia." In other words, if my impression is correct, 

 most lines will have a mean length either below 145 microns or above 

 170 microns; rarely will lines be found whose mean falls between 

 these values. Such at least has been my experience in a large 

 amount of work. Furthermore, I am inclined to believe that those 

 belonging to the smaller group (mean length below 145 microns) 

 will be found to have as a rule two micronuclei ; those belonging to 

 the large group but one micronucleus. This matter is worthy of 

 special examination. 



(e) Do tJw Diverse Lines Differ in Other Respects Besides 

 Dimensions? 



In the investigations above set forth the dimensions, and espe- 

 cially length, were made the basis of study, simply because they were 

 the characters most readily examined. Most other characteristics 

 are not easily handled in so minute and relatively undifferentiated 

 an animal as Paramecium. But there is, of course, no reason to 



