AUTHOR 8 ABSTRACT OF THIS PAPER ISSUED 

 BT THE BIBLIOGRAPHIC SERVICE, DECEMBER 6 



DEVELOPMENTAL RATE AND STRUCTURAL EXPRES- 

 SION: AN EXPERIMENTAL STUDY OF TWINS, 

 'DOUBLE MONSTERS' AND SINGLE DEFORMITIES, 

 AND THE INTERACTION AMONG EMBRYONIC 

 ORGANS DURING THEIR ORIGIN AND DEVELOP- 

 MENT! 



CHARLES R. STOCKARD 



Cornell University Medical College, New York City 



THIRTY-TWO TEXT FIGURES AND SIX PLATES 



CONTENTS 



1. Introduction 116 



2. The specific rate of development in a given species 118 



3. Continuous and discontinuous modes of development 120 



4. Experimentally changing a continuous into a discontinuous mode of 



development 122 



a. The method of experiment 122 



h. Stopping or retarding the progress of development at stages of 



apparent indifference to such interruption 125 



c. Stopping or retarding the progress of development at stages of 



critical susceptibility to such interruption 138 



d. Differences in effect between greatly reducing the developmental 



rate and actually stopping the process temporarily 154 



e. The types of arrests or deformities following a stop in development 



or a slowing of the rate 160 



5. Experimental production of twins and 'double monsters' by an earlj^ 



arrest of the developmental rate 162 



a. Arresting development by low temperature and the production of 



double embryos and twins in Fundulus 166 



h. Arresting development by reducing the oxygen supply and the 



occurrence of double individuals in the trout and Fundulus 173 



1. Results with Fundulus 173 



2. Double embryos in trout eggs 177 



c. An explanation of the frequent occurrence of twin and double chick 



embryos 186 



1 This investigation has been aided by the Memorial Foundation of St. Bar- 

 tholomew's Hospital for Diseases of the Alimentary Canal, of New York City. 

 The author expresses his appreciation for this valuable support. 



115 



