igoS.j JENNINGS— HEREDITY IN PROTOZOA. 427 



was about 120 microns; width 48 microns. Five minutes later the 

 length had increased to 132 microns, while the width was still 48 

 microns. Nine minutes later the length of the anterior product was 

 148 microns ; that of the posterior product 144 microns. The width 

 had decreased a little ; it was now about 44 microns. 



After thus increasing in fourteen minutes by nearly one fourth 

 the original length, growth became less rapid. Forty minutes later 

 (fifty- four minutes after separation) the length was about 156 

 microns. During two succeeding hours no increase in length could 

 be detected. The form was that of the normal adult, though the 

 adult size was not yet reached. 



We may summarize as follows: Some time before fission (per- 

 haps a half hour) the body shortens and thickens, so that each half 

 is at first less than half the adult length. As the constriction deepens 

 the two halves grow longer, till at the time of separation they are 

 somewhat more than half the adult length. For five to twenty min- 

 utes after separation growth in length is very rapid, while the thick- 

 ness remains stationary or decreases. Then follows a period of 

 several hours of slower growth, till the adult size is reached. 



This somewhat indefinite account, based on the observation of 

 living specimens, will now be supplemented by a statistical investi- 

 gation of a large number of individuals at various ages. The main 

 results of this statistical investigation are brought together in Table X. 



(c) Age to j Minutes {Tabic XXIX.). — A large number of 

 dividing specimens, all descendants of the individual D {caudatuin 

 form), were removed from a rapidly multiplying culture and kept 

 for from o to 5 minutes in a watch-glass of culture fluid, then killed 

 and measured. The method of work was to spend five minutes in 

 picking out dividing specimens with the capillary tube and placing 

 them in the watch-glass; at the end of the five minutes the lot was 

 killed. Then other lots were prepared in the same way. In each 

 lot killed, therefore, there occurred specimens that were in the early 

 stages of fission ; others that had separated at the moment of removal 

 and were hence just five minutes old; and all stages intermediate 

 between these two. All together, 62 unseparated pairs and 59 sepa- 

 rated individuals were secured in this way. The latter set consists 

 of individuals from o to 5 minutes old (reckoning from the moment 



