436 L. V. HEILBRUNN 



Not all of the available data were included in the curve. All 

 of the tests in table 12 were omitted. Introduction of these 

 figures would not have changed the curve. One test is included 

 which is not given in the tables. This is a twenty-second test 

 made when 5 per cent of the eggs had segmented, hence about 

 a minute before 50 per cent had segmented. 



Curve and tables show that there are three times when the 

 viscosity is high. These are just before the first polar body is 

 given off, just before the second polar body is given off, and 

 just before the completion of the first cleavage division. Thus 

 in every case immediately before the division of the cell, there 

 is an increase in viscosity. There is also a high viscosity in the 

 early stages of each mitosis. Generally the completion of one 

 division is bound up with the preparation for the next. As the 

 first polar body is given off, the second maturation spindle begins 

 to form, 3 and the viscosity increase at this time is probably 

 causally related to the appearance of the spindle. As the 

 second polar body is given off there is again a viscosity 

 increase. After the completion of the second maturation divi- 

 sion the viscosity decreases slightly. It soon rises again in 

 preparation for the cleavage spindle. As the cleavage spindle 

 forms the viscosity drops and remains low until immediately 

 before cleavage, when there is a sharp increase. In general 

 the viscosity increase at the conclusion of each mitosis is directly 

 related to the appearance of the spindle in the mitosis which 

 follows. The concluding phases of one division are bound up 

 with the initial phases of the next. The same sort of phenome- 

 non was previously found to occur in successive cleavages in the 

 sea-urchin egg. 



COMPARISONS WITH OTHER EGGS 



One point emphasized by the curve is the sudden increase 

 \j^i^ in viscosity just before division. This increase preceded divi- 



sion by a very short interval. The curve shows the interval to 

 be about two minutes or a trifle more. It must be remembered, 



2 The second maturation spindle is a new structure and does not result from a 

 transformation of the first maturation spindle. This is shown by the observations 

 of Griffin ('99), Lillie ('01), and various other observers. 



