314 



Method. 



A rubber tube connected the water-tap with a long glass tube. 

 The latter tube was placed in a tall (450 X 85 c.) glass jar, and 

 extended nearly to the bottom of the jar. When the water was turned 

 on, and the jar filled, a circular current was started at the bottom. 

 When a mass of eggs was put into the jar it was caught by this 

 current and whirled over and over in a most irregular way. The 

 whole mass of eggs rotated once in every 5 to 15 seconds. It could 

 be readily seen that the eggs did not revolve in any one constant 

 plane, but in a most irregular, and ever changing series of revolutions. 



The toad was killed and the long strings of eggs were removed 

 from the uterus and put at once into a small jar of water which was 

 kept constantly whirling around by my assistant. Sperm was added 

 and for half an hour the eggs were kept constantly turning over and 

 over with great irregularity and with considerable rapidity. After half 

 an hour the eggs were placed in the jars described above where they 

 remained throughout the remainder of the experiment. 



Results. 

 The cleavage of the rotating eggs progressed normally as was 

 determined by removing a few of the eggs at intervals. These eggs 

 were, of course, not returned to the jar. Eggs removed at the two 

 cell stage (after 5 hours) and kept outside developed normally. Eggs 

 removed after 25 and 36 hours also produced normal embryos. After 

 48 hours the eggs, that were still rotating, also showed the dorsal lip 

 of the blastopore. The eggs were kept rotating for several days 

 longer and produced normal embryos. 



Conclusions. 



The results show that gravity need not be a determining factor 

 in the development of a bilateral plane in the apparently radially 

 symmetrical egg. It should be carefully noted that I do not claim 

 that gravity may not under certain conditions produce this result, but 

 that if gravity, as a constant factor, is eliminated a bilateral plane is 

 nevertheless developed. The burden of proof lies, therefore, with those 

 who claim that there is a necessary connection between the action of 

 gravity on a resting egg and the appearance of a median plane of 

 symmetry in the egg. 



W'hen the egg of the frog (Rana palustris) is removed from the 

 ovary there is no sign of the grey streak [Schultze ^)] or white 



1) Schultze, Archiv f. mikr. Anat., Bd. 56, 1900. 



