THE DEVELOPMENT OF THE PROOTIC HEAD 



SOMITES AND EYE MUSCLES IN 



CHELYDRA SERPENTINA 



CHARLES EUGENE JOHNSON 



From the Laboratory of Comparative Ayiatomy of Vertebrates, Department of 

 Animal Biology, University of Minnesota 



TWENTY-FOUR FIGURES (tEN PLATES) 



CONTENTS 



Introduction 119 



Review of literature 121 



The head somites 121 



The eye muscles 126 



Descriptive part : material and methods 128 



The head somites 129 



3.5-mm. embryo 129 



4-mm. embryo 133 



4.5-mm. embryo 136 



5-mm. embryo 137 



6-mm. embryo 139 



7-mm. embryo 141 



8-mm. embryo ^ 142 



Summary 143 



The development of the eye muscles 144 



9-mm. embryo 144 



10-mm. embryo (a) 146 



10-mm. embryo (b) 149 



11-mm. embryo 149 



Chelydra embryo 152 



Summary 155 



Literature cited 163 



INTRODUCTION 



Balfour ('78), working on elasmobranch embryos, was the 

 first to observe that the separation of the mesodermic layers 

 which gives rise to the body cavity of the trunk, extends for- 

 ward into the head, ar.d forms a cavity which later becomes 



119 



THE AMERICAN JOURNAL OP ANATOMY, VOL. 14, NO. 2 

 JANUARY, 1913 



