Physiology. — "Ejfects of th>. Rai/s of Radium on the. Oogenesis 

 of Daphnia pulex\ By Miss M. A. van Hkrwehukn. M. D. 

 (Communicated by Prof. C. A. Pkkki-hahing.) 



(Communicated in the meeting of Sept. 29, 1918). 



For a considerable time I have been prosecuting the effects of 

 radium radiation on a race of Daphnia pulex bred in the laboratory, 

 with whose method of reproduction I had become thoroughly ac- 

 quainted during a study of rather more than B years. My original 

 purpose was to evoh e, if possible, [)arthenogenesis in the sexual 

 period, or conversely, to impart to the parthenogenelic females the 

 faculty of producing a sexual offspring. The importance of this 

 experimentation wat> sufKlciently borne in upon me in connection 

 with the view adopted by many researchers that by radiating the 

 organism with radium, enzymic actions are accelerated or diverted. 

 A short or a j)rolonged radiation with 0,7 mgrs or 3, J mgi's of 

 radiumbromide, at my disposal, never resulted in any effect upon 

 the sexual or the parthenogenetic stage, whereas after a radiation 

 with a stronger pre|)aralion the animals succumb. ') Nevertheless I 

 considered it a point of importance to continue the experiments, 

 since they throw a peculiar light upon tlie resistance of the proto- 

 plasm in the several phases of the oogenesis and of the embryonic 

 development under the influence of radium rays. 



Daphnia pulex affords extremely fit material foi- such expei-iments. 

 Besides being fairly transparent and easy to watch under the micros- 

 cope, it also enables us not only to follow in the living animal the 

 development of the [)arthenogenetic eggs located in the broodpouch, 

 but also to determine the degree of maturation of the eggs in the 

 ovary. Sometimes the amount of yolk in the maturing eggs enables 

 ns to foretell correctly to a few hours, when they will leave the 

 ovary. There is always plenty of material for control, as several 

 young ones can be expected at every parturition. Over and above, 

 the rapid succession of generations grants a comprehensive survey 

 not only of the animals under examination, but also of a large 

 progeny. 



1) Verslag "Koninklijke Akad. v. Wetenschappen" Deel XX p. 20. 



