Vol. XXXVII. August, IQIQ. No. 2 



BIOLOGICAL BULLETIN 



STUDIES IX THE LIFE CYCLE OF SIMOCEPHALUS 



VETULUS. 



WVMAN REED GREEN. 

 HULL ZOOLOGICAL LABORATORY. 



CONTEXTS. 



PAGE. 

 I. Introduction *g 



II. Literature Review 51 



III. Material 56 



IV. Isolation Experiments .... 



1. Isolation of Females from General Cultures 57 



2. Experiments with Food and Culture Media 58 



3. On Isolated Stem Mothers 62 



4. Temperature Experiments. . . 67 



5. Miscellaneous Experiments. ... 69 



V. Experiments on Ephippial Eggs 71 



1. Evaporation Experiment with NaCl 



2. Effect of Freezing in Nature 72 



3. Effect of Low Concentrations of H'jSO^ and KOH. . . . 



4. Effect of Successive Freezings 



5. Effect of Injury or Removal of Ephippia. . . 



6. Effect of Long Retention in Water 



7. Experiment on Eggs of Daphnia pidex 



8. On the Hatching of Seventy Stem Mothers 75 



VI. Observation on Pairing ... 76 



VII. General Discussion . . . . 81 



1. Relation of Males to Sexual States in the Females. . 81 



2. Effect of the Sexual Phase on the Females 81 



3. Relation of Age to the Kind of Offspring. . . 



4. Significance of Mixed Broods 83 



5. Relation of Sexuality to Senescence of Cultures .... 84 



6. Effect of External Factors Upon the Life Cycle 88 



VIII. Summary 



IX. Bibliography. . . . 



I. IXTRODUCTIOX. 



These studies on Simocephnlns were begun at the Hull Zoologi- 

 cal Laboratory of the University of Chicago, in 1913. The 

 life cycle is very complex and has not been worked out satis- 



49 



