The Energy of Segmentation 3^^ 



there are present in such a solution two osmotic pressures, due 

 respectively to the salts in the sea-water and to the sugar in solu- 

 tion, and these pressures are additive and in that respect inde- 

 pendent, the natural environment of the eggs is retained, and so, 

 as constant, is eliminable; therefore will our concern be with the 

 pressure of the sugar alone, as if it were isolated; and, secondly, 

 any specific chemical action of the sugar solution can be regarded 

 as eliminated, since it is shown from various experiments that for 

 this urea, or glycerine, or, perhaps any other non-electrolyte, can 

 be substituted. 



The typical method of experimental procedure, of which the 

 concrete results will be presented below, then, was as follows: A 

 § mol. pure cane sugar solution in sea-water, the sugar having 

 been previously carefully dried, was prepared; and sea-urchin eggs 

 in excellent condition were selected and fertilized. Then, about ten 

 minutes before cleavage might be expected to begin, these fertilized 

 eggs were transferred to finger-bowls containing sugar solutions in 

 a graded series of concentrations obtained by diluting definite 

 amounts of the standard §m. solution with definite amounts of sea- 

 water. Furthermore, the sea-water used in transferring the eggs 

 was in each case accurately measured with a pipette and included 

 in the computation, as was also the room temperature. Prelimi- 

 nary and control experiments had shown, too, that in the trans- 

 ferring of the eggs to these solutions, the period elapsed after fer- 

 tilization was largely a matter of indifference; however, they were, 

 in fact, transferred at the time stated in order to prevent the occur- 

 rence of cytolysis. During the experiment, especially while seg- 

 mentation was taking place, it was necessary to make frequent and 

 rapid observations both of "experimented" eggs and of control; 

 for thus only could it be found which solutions were of a strength 

 either just sufficient to inhibit the cleavage or just weak enough 

 to allow it to proceed; observation was at this time necessary also 

 for the reason that, since after some time nuclear division takes 

 place in some cases, later observations as to the inhibiting point 

 are, in general, not of as great reliability and accuracy as are those 

 which are conducted as above. Now it is evident that, by such a 

 method, there could be found with considerable accuracy a point 



