igos.i . JENNINGS— HEREDITY IN PROTOZOA. 495 



identical conditions. The differences are fully as marked as those 

 found among diverse lines derived from individuals not conjugating 

 and taken without reference to the period in the life cycle in which 

 they happen to be. 



Besides this general result on our main problem, the following 

 important facts are brought out by the table : 



1. The six lines derived from the six different pairs (first six of 

 the table) are clearly distinct. They show parallel diff"erences in 

 both sets of tests ; the order of dimensions from largest to smallest 

 is the same in both the first and the second measurements, though 

 these are separated by at least fifteen generations. 



2. The two lines, Fi and F2, derived from single ex-con jugants, 

 are likewise distinct from each other. So far as the measurements 

 go, F I may possibly be the same as Ai, F2 as A2. 



3. Certain different sets are likewise found in the other lots of 

 the table. 



4. The different sets fall into two very distinct groups, whose 

 dimensions are separated by a wide interval. To the large group 

 belong L2, Gi, Ai, A2, Fi, F2 and D. To the small group belong 

 the others. The greatest mean length of any set of the smaller 

 group (140.800 microns) differs widely from the least mean length 

 of any set of the larger group (176.901 microns). These two groups 

 correspond in general to what we have heretofore called the " aiirelia 

 form " and the " caudatum form." 



As there was no danger of confusing any lot of the larger group v. ith 

 any lot of the smaller one, the second measurements of the two groups were 

 not made for the same day ; the lots of the larger group were killed March 

 13, while those of the smaller group were not killed till March 19, as the 

 table shows. This was done on acount of the great labor involved in select- 

 ing, with capillary pipette, killing properly, and preserving, so many different 

 sets on the same day. This difference of treatment of course does not alter 

 the comparability of the different sets within a given group, which is all that 

 we require. 



5. How shall we decide which of the thirteen different sets form 

 distinct lines? For this it will be best to take into consideration 

 mainly the length, since we know from our earlier studies that little 

 significance is to be attached to difference in breadth, owing to the 

 extreme chanoes in that dimension with slight dift'erences in food. 



