xgo8.] JENNINGS— HEREDITY IN PROTOZOA. 439 



four hours. As a result of this treatment they did not grow so 

 rapidly as did the twelve- and eighteen-hour lots, and are smaller 

 than these. The purpose in studying this group (as well as other 

 groups) was mainly to determine the variability and the correlation 

 between length and breadth. Both are less, as Table X. shows, than 

 is usually the case in random samples. 



The specimens 12, 18 and 24 hours old may be taken as types of 

 adult Paraniccia of this strain (progeny of D ; candatuin form) 

 before the changes leading to fission have begun. 



Diagram 4 gives polygons of variation for the different ages, in 

 descendants of D, as compared with a random sample ; it shows 

 clearly the part played in the observed variations by the presence 

 of different stages of growth. 



Sixth Stage: Preparing for Fission. 



As Table X. shows, the adults of the progeny of D (caitdatnin 

 form) reach a mean length of 168.532 to 199.048 microns (rows 2^ 

 and 22) under the cultural conditions employed, while the mean 

 breadth varies from 40.320 (row 23) to 62.796 microns (row 20). 

 But the maxinnun length is (under the same conditions), of course, 

 much greater than the mean. In the random samples we find indi- 

 viduals up to 224 microns in length and 88 in breadth (see, for 

 example. Table LI.) ; and among those 18 hours old (Table XL.) 

 we find a length of 228 microns. 



Now, when we compare these large adults with the specimens 

 actually beginning fission (which are supposedly the oldest of all), 

 certain peculiar facts appear. The specimens beginning fission are 

 hy no means the longest of the lot; a given culture contains many 

 specimens much longer than those showing the first signs of division. 

 Thus, in the " Lot i " of Table VIII. , we find 131 specimens in the 

 very earliest stages of fission (Table XIII., page 442). The mean 

 length of these is 175.696 microns (row 25, Table X.), and the 

 longest specimen is 204 microns long. But in the random sample 

 of the specimens that are not dividing, from this same lot (taken at 

 the same time) the mean length is 199.960 microns (row 2y, Table 

 X.), and certain individuals reach a length of 240 microns (Table 

 XIV., page 443)- Of the two hundred specimens of the random 



