CHARACTERISTICS OF THE DIVERSE RACES OF 



PARAMECIUM 



H. S. JENNINGS and GEORGE T. HARGITT 



From the Zoological Laboratory, Johns Hopkins University 



TwENTY-rotJR Figures 



CONTENTS 



Introduction * 496 



Part 1. Number and structure of the micro-nuclei, and the species question. 497 

 Part 2. Other characteristics of the diverse races 509 



1. Differences in size and their permanence 509 



2. Similarities and differences of the various races in form and 



structure 522 



Form ' 522 



Posterior tuft of long cilia 528 



Trichocysts 531 



Contractile vacuoles 531 



Summary 532 



3. Differences among the diverse races with respect to conjuga- 



tion 532 



4. Differences in rate of fission among the different races 533 



5. Differences in cultural requirements, and other physiologi- 



cal differences 538 



6. Relation of the races to the described species of Paramecium 541 



7. Indications of the existence of diverse races of Protozoa in 



the reports of other observers 544 



8. Diverse, closely related races in other organisms 547 



9. Origin of the diverse races 549 



10. List of the races or lines dealt with in this paper, with their 



characteristics 558 



1. Caudatum group 556 



2. Aurelia group 557 



11. Precautions necessary for work with pure races 557 



