From the Zoological Laboratory of Johns Hopkins University 



HEREDITY, VARIATION AND EVOLUTION IN 

 PROTOZOA 



I THE FATE OF NEW STRUCTURAL CHARACTERS IN PARAME- 

 CIUM, IN CONNECTION WITH THE PROBLEM OF THE 

 INHERITANCE OF ACQUIRED CHARACTERS IN UNICELLU- 

 LAR ORGANISMS 



BY 



H. S. JENNINGS 



With 22 Figures 



Introduction 577 



1 Object of the work 577 



2 General plan of the investigation and principles guiding it 578 



3 Place of the present investigation in this plan 583 



Assumed difference in heredity between unicellular and multicellular animals 584 



The fate of new structural characters ("acquired characters'') 586 



1 Localized and unlocalized characters 586 



2 Typical examples of inheritance and its problems in the Protozoa 586 



The fate of new localized structures in Paramecium, with observations on growth and regulation .... 589 



1 History of a large new append age 589 



2 General relations and processes shown in the history of the new structure 599 



3 The fate of other new structures in reproduction 604 



a Points, spines or appendages 604 



h Anterior end truncate 607 



c Posterior part of the body truncate or lacking 608 



d Anterior end with a projecting angle 609 



e Crookedness or general irregularity of form 609 



/ Behavior of mutilations in reproduction 614 



4 Acquired characters that tend to be inherited 618 



g Acquirement and inheritance of a tendency for the adults to remain united in chains. . . .618 



Effects of artificial selection 620 



Effects of natural selection 621 



What must be the nature of a new character, that it may be inherited .'' 622 



Examples of modifications from which new inherited characters might result 624 



Summary and general discussion 625 



Literature cited 632 



INTRODUCTION 



I Object of the PFork 

 The investigations of which the first instalment is here pre- 

 sented are designed as the beginning of a study of the problems 



The Journal of Experi.ment.'Vl Zoology, vol. v, no. 4 



