UNIVERSITY OF CALIFORNIA PUBLICATIONS 



IN 



ZOOLOGY 



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



CONTRIBUTIONS FROM THE LABORATORY 



OF THE 



MARINE 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 Growth Stages ........................................................................................ 200 



External Features. Period I .............................................................. ....... 200 



Egg .......................................................................................................... 200 



First to Sixth Cleavages ...................................................................... 201 



Comparison of D. pusillus with Amphioxus and with Ascidia 

 (dona 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 Amphioxus with reference to Origin of 

 Body Cavities ................................................................................................ 213 



Bibliography ............................................................................................ - ........... 216 



