547 



Prior to maturity Daphniae resist radium radiation for a long- 

 time. Only after a sojourn of many hours on the capsule with 0,7 

 mgrs of radium bi'omide the future ripening of the oögonia is also 

 endangered. 



A microscopic* examination of the ovary and the embryos reveals 

 that the deleterious elïect of radium manifests itself only towards 

 the close of the blastu la-stage by an abnormal behaviour of (he 

 chromatin, also when the egg-cells were atfected when lying still in 

 the ovary. 



If the beta-rays are eliminated through filtration the deleterious 

 effect of radium is arrested or highly diminished, which [)ioves the 

 beta-rays lo be mainly responsible for the desti-iiction of the eggs. 



36 



Proceedings Royal Acad. Amsterdam. Vol. XXI. 



