408 JENNINGS— HEREDITY IN PROTOZOA. [April 24, 



selected the cultures descended from the individual D ; while the 

 progeny of c represented the aurelia group. Now, from each of 

 these groups the largest and smallest individuals were isolated and 

 allowed to multiply, under uniform conditions. Thus, the selected 

 large and small individuals of a given group were all progeny of a 

 single individual, forming thus a "pure line"; this fact is of great 

 importance, as the sequel will show. 



A large number of experiments gave throughout negative results. 

 The progeny of large and of small individuals (within a given pure 

 line) shelved no characteristic differences in size. Large specimens 

 of the caudatum form produced progeny on the whole no larger 

 than those produced by small specimens of the same form, and the 

 same was true in the aurelia group. In many experiments a single 

 large and a single small specimen were isolated, and their progeny 

 compared ; in other cases a number of large specimens were placed 

 together in one vessel, a number of small ones in another, and their 

 progeny compared after lapse of a considerable period. Since the 

 results of these experiments were throughout negative, I will give 

 the details of but a single illustrative experiment : 



On July 27 ten large and ten small specimens were selected from 

 a lot of the caudatum group, all being descendants of a single indi- 

 vidual D. The ten large specimens measured, as nearly as could be 

 determined while alive, approximately 250 microns each, and were 

 thick in proportion to the length. The ten small specimens were 

 about 150 microns long, and were thin. The two sets were placed 

 in equal quantities of the same culture fluid. 



At the end of three days the large set had produced many indi- 

 viduals. Fifty of these taken at random gave a mean length of 

 189.040 microns, a mean breadth of 60.560 microns. 



The smaller individuals did not increase rapidly and five of them 

 died before dividing, so that all the progeny came from six indi- 

 viduals. The six increased in size before dividing. At the end of 

 three days there were twenty-one individuals. The mean length 

 was 205.140 microns, the mean breadth 56.570 microns. 



Thus the smaller specimens had produced progeny that were a 

 little longer, but not quite so broad, as those resulting from the 

 larger set. The existing differences are clearly without significance. 



