468 JOHNSON. [Vol. VIII. 



D. Conjugation 527 



1. External Phenomena 527 



2. Nuclear Phenomena 528 



E. Teratology 531 



IV. Biology and Physiology 535 



A. Rate of Multiplication 535 



B. Relative Vitality of Large and Small Stentors 540 



C. Nutrition; Alimentary Vortex 542 



D. Defecation; Position of Anus 544 



E. Contractile Vacuole 547 



F. Merotomy 548 



V. Literature cited 552 



I. Introduction. 



Occupying a place about midway between the lowest and 

 the most highly-organized of the Ciliate Infusoria, and possess- 

 ing in large measure the characteristics of both free-swimming 

 and sedentary forms, the genus Stentor may well serve as type 

 of its Class. Their abundance, large size, and strongly-marked 

 morphological characters have made the Stentors favorite sub- 

 jects for study with zoologists ; and in recent years one species, 

 Stentor ccsruleus, has been repeatedly used in cytological re- 

 search, particularly in experimental work undertaken to ascer- 

 tain the physiological role of the nucleus. 



In the present paper observations upon five species of 

 American Stentors are recorded. All have been obtained in 

 abundance except Stentor rocselii, which, not being gregarious, 

 cannot be collected in large numbers. 



The work began with a study of the nuclear changes of 

 .S. cceriileus at time of fission, undertaken at the suggestion of 

 Prof. E. L. Mark, when I was under his instruction at the 

 Zoological Laboratory of Harvard University. The scope of 

 the work was afterwards extended, and the investigation of 

 several phases in the life-history of the Stentors was carried 

 on at Williams College, at the Marine Biological Laboratory, 

 Wood's Holl, Mass., and at Clark University, Worcester, Mass. 



Material has been obtained from four widely-separated locali- 

 ties in Massachusetts : Cambridge, Williamstown, Falmouth, 

 and Worcester. Each locality has yielded in abundance some 



