AUTHOR S ABSTRACT OF THIS PAPER ISSUED 

 BY THE BIBLIOGRAPHIC SERVICE, OCTOBER 17 



THE CONDITIONS FOR CONJUGATION IN DIVERSE 

 RACES OF PARAMECIUM 



TIOYT 8. HOPKINS 

 Zoological Laboraiory of Ihc Johns Flopkins Univcrsilij 



CONTENTS 



Introduction ■ . . . 339 



Material and methods 344 



1 . Conjugation in diverse strains 347 



a. Paramecium caudatum 347 



b. Paramecium aurelia 356 



2. Growth factors influencing conjugation 368 



General summary 374 



Literature cited 376 



INTRODUCTION 



Maupas ('89) was one of the first to suggest differences be- 

 tween nearly related species of Infusoria in respect to their 

 tendency to conjugate. He found, for example, that Colpidium 

 colpoda would conjugate more readily than the similar species 

 C . truncatum. Like differences have been shown by later inves- 

 tigators to obtain in other genera, as in the two species of Colpoda 

 studied by Enriques ('08). It had long been known, too, that 

 cultures of the same species differ much as regards susceptibility. 

 Most authors attributed these differences to environmental 

 factors, as mixed cultures of uncertain derivation were used in 

 most cases. As pure, or 'j^edigreed,' races began to be used, 

 these cultural diversities were conceived of as having possibly 

 a racial basis. If diversities with respect to size, shape, and 

 division rate have their origin in heredity, ma}^ it not be that 

 differences in the ability to conjugate are based upon hereditary 

 factors? 



This view has led to some controversy in recent years in regard 

 to the existence of so-called 'non-conjugating races,' calling 

 into question the universality of fertilization among the Infusoria. 



339 



