THE LIFE CYCLE OF OITHONA NANA, 

 REARED EXPERIMENTALLY 



BY 



HELEN E. MURPHY 

 (Contribution from the Scripps Institution for Biological Research) 



CONTENTS 



PAGE 



I. Introduction - 4411 



H. Rearing experiments 449 



III. Stages of development 451 



IV. Conclusion 454 



I. INTRODUCTION 



An examination of a series of surface collections of zooplankton 

 made at the pier of the Scripps Institution, La Jolla, California, 

 indicates that Oithona nana is numerically the dominant Copepod 

 throughout the year. The possibility that this is a hardy species, 

 together with the fact that no single specimen of marine copepod has 

 been bred through the successive stages from egg to adult, led to 

 rearing experiments, the results of which are summarized in the 

 present paper. 



II. REARING EXPERIMENTS 



Bearing jars. — Flat-bottomed glass stender dishes 60 mm. in 

 diameter and 30 mm. hisi'li were used as rearing jars. These proved 

 to be large enough for proper growth of the specimens, and were 

 easily oriented on the stage of the binocular microscope. Unnecessary 

 handling of specimens was thus eliminated. The containers were two- 

 thirds filled with unfiltered ocean water and placed in indirect north 

 light. Except for a slight addition to compensate for evaporation, 

 the water was unchanged during the entire experiments. Fundus 

 growth was controlled by increasing the intensity of light. Strong 

 light caused the specimens to become very agitated. To prevent this, 

 a portion of the jar was always kept shaded. A piece of fresh kelp 

 about 1 mm. scpiare was added to each jar and allowed to remain for 



