RHYTHMICAL SUSCEPTIBILITY OF SEA URCHIN EGGS. 259 



In normal fertilization the sperm cell which fertilizes the egg 

 accomplishes two things of immediate importance, viz., starts 

 division and prevents the production of toxic substances during 

 cleavage or inhibits their action. It is therefore impossible 

 for the hypertonic sea water to exercise its protective action 

 upon the normally fertilized egg. It can affect the egg only 

 injuriously. Our experiments show that this injurious action of 

 the hypertonic solution is most pronounced just preceding and 

 during cytoplasmic division, and that such action is very slight 

 immediately afterward. 



In the case of artificial parthenogenesis the hypertonic treat- 

 ment is much shorter than in the experiments just described, 

 and hence we may consider its injurious effects excluded. The 

 Curve I. representing the results of Table II. shows the rhyth- 

 micity of the beneficial effect of the hypertonic treatment, 

 while the curve constructed from Table III. indicates only 

 injurious effects. There is therefore no reason why the two 

 curves should be identical in character, although each shows a 

 rhythmicity of susceptibility to the action of hypertonic sea 

 water. 



According to Loeb the artificial membrane ■ formation in 

 artificial parthenogenesis starts the chemical phenomena which 

 give rise to the process of cell division and development; but 

 the process is incomplete or abnormal and leads to the disintegra- 

 tion of the egg unless a second treatment is added, usually a 

 treatment with hypertonic sea water. Since, by the membrane 

 formation, chemical or physico-chemical changes induced in the 

 egg are rhythmical, it is intelligible that it should make a differ- 

 ence in which stage of the cycle the treatment with the hypertonic 

 solution is supplied. This is presumably the explanation of 

 Herlant's observation. 



In conclusion I wish to express my best thanks to Dr. Frank 

 R. Lillie for so generously giving to me the privileges of the 

 Marine Biological Laboratory at Woods Hole, and to Dr. 

 Jacques Loeb for much helpful advice and criticism. 



