258 ' ARTHUR RUSSELL MOORE. 



Table III. 



T° = 20°. 

 Time in normal sea water 



after fertilization 5 I5 25 35 45 55 65 75 85 95 105 115 125 135 145 155 



Blastulee per cent 50 50 95 95 90 72 74 87 91 73 80 91 91 71 86 89 



The character of the curve constructed from Table III. 

 differs from that made from the data of Table II. It will be 

 noted that in the latter case there is an early maximum and 

 minimum, and a slight secondary maximum reached at about the 

 time cleavage would take place if the eggs had been normally 

 fertilized. The dissimilarity may be due to the fact that the 

 hypertonic solution may have two effects on developing eggs, 

 viz., beneficial and injurious. We have seen that the acid 

 treatment alone leads to the early stages of development, and 

 that if the temperature is kept low the eggs of S. purpuratus 

 develop to the early blastula stage. But before the gastrula 

 stage is reached, the embryos go to pieces. To all appearances 

 the early morula stages are quite normal. Loeb has suggested 

 that cleavage may be accompanied by the production of toxic 

 substances which, accumulating with each successive division, 

 cause the larvae to sicken and die. The injurious effects of these 

 substances may be prevented by treatment of the egg with a 

 hypertonic solution, or the formation of the injurious substances 

 may be inhibited by long hypertonic treatment before membrane 

 formation. It has been shown that simply by preventing oxida- 

 tions for a time instead of treating the eggs with hypertonic 

 sea water, normal development may be secured. Hence, the 

 hypertonic solution or lack of oxygen exercises a beneficial or 

 curative effect on parthenogenetically developing eggs and allows 

 the embryo to develop to maturity. 



On the other hand there is an optimum time for the continuance 

 of the action of the hypertonic solution, and if the exposure is 

 continued longer the solution acts deleteriously and as a result 

 development stops and the egg disintegrates. It becomes clear 

 then that the hypertonic treatment may have one of the two 

 opposite effects upon the egg, i. e., beneficial or injurious, depend- 

 ing upon the duration of the treatment, or in other words upon 

 the condition of the egg when treated. 



