38 GEORGINA B. SPOONER 



In table 2 are set down the results of a series of experiments in 

 which the unfertilized eggs of a single female were centrifuged at 

 a high rate of speed, 6000 to 7000 revolutions a minute, during 

 different periods of time, varying from one-half to three minutes. 

 The result of this experiment may be taken to indicate a slight 

 increase in mortality over the controls due to longer periods of 

 centrifuging. The increase, however, is comparatively slight and 

 not perfectly regular. Moreover, when the numbers of normal 

 and abnormal eggs from several experiments are put together as 

 in table 3 no such consistent rise in mortality is apparent. 



The evidence, I believe, shows that there is no direct relation 

 , between the percentage of mortality and either the duration of 

 the force or the stage in development at which the eggs were cen- 

 trifuged. The counts from several series of experiments have been 

 put together in table 4, and it is interesting to see that the per- 

 centage of mortality among the gastrulas in the centrifuged eggs 

 does not vary greatly from that of the controls. Such variation 

 as does occur is not consistent and may easily be due to error in 

 counting. 



Direction of cleavage after centrifuging 



In regard to the development of the eggs after centrifuging, 

 Lyon and Morgan found that in the majority of cases the first 

 cleavage was perpendicular to the stratification, while the later 

 gastrula pole bears no definite relation to the layers. By isolat- 

 ing eggs and recording their development to the gastrula stage, 

 I found, 1908, that gastrulation takes place at the micromere 

 pole as in normal eggs and is quite independent of the centrif- 

 ugal layers. At the same time by use of Boveri's india ink method 

 Morgan showed that the micromeres form approximately oppo- 

 site the micropyle. This is the relation which Boveri describes 

 for the normal egg of Toxopneustes except that he speaks of the 

 micromeres as being exactly opposite the micropyle. The ques- 

 tion of the exactness of the relation became interesting because 

 the cleavages so evidently conform to the stratification of the 

 centrifuged egg. Therefore I studied, last summer, a set of nor- 

 mal eggs in india ink solution and found that the relation between 



