AUTHOR S ABSTRACT OF THIS PAPER ISSUED 

 BT THE BIBLIOGRAPHIC SERVICE, OCTOBER 13 



AN EXPERIMENTAL STUDY OF AN AMICRO- 

 NUCLEATE OXYTRICHA 



II. THE FORMATION OF DOUBLE ANIMALS OR 'tWINS'^ 



J. A. DAWSON 



Osborn Zoological Laboratory, Yale University 



TWENTY-TWO FIGURES 



CONTENTS 



I. Introduction 129 



II. Material and methods 131 



III. The occurrenice and behavior of double animals 132 



IV. Experiments on pedigreed 'twin' cultures 



a. History of culture AT (series I) 136 



b. Effect of selection on 'twins' 138 



V. Study of the origin of 'twins' 141 



VI. Discussion 149 



VII. Summary and conclusions 152 



1. INTRODUCTION 



The occurrence of double animals, or as they are usually 

 termed, double monsters, is not uncommon among the Infusoria. 

 Although they most frequently occur during experiments where 

 merotomy has been practiced, yet the 'spontaneous' occurrence 

 of such forms has been noted several times. 



The first observations of importance in respect to formation 

 of double animals were made by Balbiani ('91), working with 

 Stentor, who described two monsters, one of which was formed 

 from a posterior 'merozoite' which was again cut longitudinally 

 in the posterior end. Traces of duality were seen after the first 



1 It is realized that there are certain objections involved in the use of the word 

 twin as applied here, but inasmuch as there is apparently no single English word 

 which is more suitable, this term is used at present to designate the double animal. 



129 



