No. 3.] BIOLOGY OF THE STENTORS. 539 



undisturbed for weeks. I had originally placed in it a large 

 number of Blue Stentors from an unusually rich gathering 

 collected in Alewife Brook, Cambridge. The culture had not 

 done well, apparently from lack of food, and I believed that it 

 had become barren. Examination showed that it contained a 

 few Stentors of unusually large size and splendid development. 

 The cytoplasm was very free from food-vacuoles, and it was 

 evident that they had had a meagre diet for a considerable 

 time. This I believe to be the prime cause of their large size 

 and fine development — a regimen sufficient to maintain Hfe 

 and admit of growth, but not generous enough to promote 

 fission. Several of the Stentors were placed in a watch-glass 

 which already contained an abundant growth of Scenedesmus, 

 upon which they fed. Fission took place only at long intervals, 

 and the large size of the progenitors was maintained in their 

 descendents. 



It will perhaps be claimed that the large size and fine 

 condition of the Stentors above-described was due, not to 

 meagre diet, but to the fact that they were the survivors of a 

 much larger number, and according to the doctrine of natural 

 selection, must have been the most vigorous and best able to 

 cope with adverse conditions. There is certainly something to 

 be said in favor of this view. But an experiment hereafter to 

 be described (see p. 540) has shown that the largest Stentors 

 are not necessarily the most vigorous or prolific, and another 

 experiment has demonstrated that it is possible to take Stentors 

 of average size or less, put them on a scanty vegetable diet, 

 and obtain large and finely-developed specimens. The details 

 of the latter experiment are as follows : On Jan. 15, 1892, I 

 found a Stentor (of about average size) in fission, which showed 

 the division of the meganucleus at time of condensation. I 

 placed its offspring in water which contained a growth of 

 minute algae. On the i6th another Stentor, also of average 

 size, was found, and it likewise exhibited the early division of 

 the nucleus. Its offspring were placed with the others, the 

 object being to ascertain whether the early division of the 

 nucleus would reappear at subsequent fissions. The original 

 four Stentors had increased to six on the i8th and to eigrht on 



