UNIVERSITY OF CALIFORNIA PUBLICATIONS 



IN 



ZOOLOGY 



Vor. 4, No. 3, pp. 187-226, Pis. 4-8 March 31, 1908 



CONTEIBUTIONS FKOM THE LABOEATORY 



OF THE 



MAEINE BIOLOGICAL ASSOCIATION OF SAN DIEGO. 



XIX 



THE EARLY LIFE-HISTORY OF DOLICH- 



OGLOSSUS PUSILLUS RITTER. 



BY 



B. M. DAVIS. 



CONTENTS. 



PAGE 



Introduction 188 



Periods of Development 190 



Early Habits and Activities of D. pusillus 192 



Period I 192 



Period II 192 



Period III 194 



Periods of Development Correlated with Habits and Distribution of 



Adults - 195 



Early Grovvtli Stages 200 



External Features. Period I 200 



Egg 200 



First to Sixth Cleavages 201 



Comparison of D. pusillus with Amphioxus and with Ascidia 



(Ciona intestinalis) in their Early Cleavage 203 



Blastula ■■-- 204 



Gastrula -^-- 204 



Larva within the Egg-capsule 205 



Period II 205 



Period III 205 



Internal Features. Period I 205 



Blastula 205 



Gastrula - 206 



Mesoderm and Body Cavities 207 



Gland Cells 212 



Occurrence of Half Embryos and Double Embryos 213 



Comparison of D. pusillus and Ampliioxus with reference to Origin of 



Body Cavities -1"^ 



Bibliography -1" 



