Volume XIII . April, l8gy. Number I. 



JOURNAL 



THE EMBRYOLOGY OF CREPIDULA, 



A CONTRIBUTION TO THE CELL LINEAGE AND EARLY 

 DEVELOPMENT OF SOME MARINE GASTEROPODS. 



EDWIN GRANT CONKLIN, 

 Professor of Comparative Embryology, University of Pennsylvania. 



CONTENTS. 



PAGE 



A. Introduction 3 



1. Purpose and History of the Work 3 



2. Methods 7 



B. The Genus Crepidula 9 



1. Natural History 9 



2. Breeding Habits IS 



3. Types of Development in Crepidula fornicata, C. plana, C. convexa, 



and C. adunca 17 



4. General Sketch of the Embryology 25 



5. Abnormalities 3° 



C. History of the Cleavage 33 



Nomenclature 33 



The Unsegmented Ovum 3^ 



I. The Primary Cleavages 40 



1. The First Cleavage 4° 



2. The Second Cleavage 44 



3. The Origin and Significance of the Polar Furrows 44 



4. The Axial Relations of the First Two Cleavages 53 



