95 



Experiments on Developing Eggs. 



A. J. BiGNEY. 



The greatest mysteries in the biological world are undoubtedly locked 

 up in the egg. If we can understand the intricate changes that go on in 

 a developing egg Ave have accomplished much. Considerable light has been 

 thrown upon this subject during the past few years. Eminent biologists 

 all over the world are spending their lives trying to solve the mysteries. 

 A'arious experiments have been devised to try to throw light upon these 

 early chauges in the egg. 



These experiments which I performed were under the direction of Dr. 

 Lillie, of the Chicago University, at the Woods HoU Marine Laboratory. 



Experiment 1. — The egg of a common sea minnow, the Fundulus. was 

 used. When the egg was in the two-celled stage one of the blastomeres 

 was punctured with a needle and pressed out of the vitelline membrane. 

 The other blastomere went on developing. Its development, however, 

 was slower. It went through all the regular changes and became an em- 

 bryo. The only difference that could be discerned was in size. It was 

 considerably smaller than the normal embryo. I succeeded in keeping it 

 alive seven days. I have not studied the embryo any more to see whether 

 there -are internal changes that are different from the normal embrj'o. 

 The significance of this ability of one Olastomere to develop into a com- 

 plete embryo is not fully understood. In this egg it seems to indicate that 

 the developing power is equally distributed throughout the egg. 



Experiment 2.— lu this experiment the eggs of the sea-urchin Arbacia 

 were used. The eggs just fertilized were placed under a long cover-glass 

 with a thin piece of cover-glass under one end, thus giving a graded i^res- 

 sure upon them. In the segmentation of these eggs the first and second 

 cleavage planes were natural, but the third was parallel to the first, the 

 same as in the Fundulus. The blastoderm in the eight-celled and sixteen- 

 celled stages were almost identical with corresponding stages of Fundu- 

 lus. The eggs did not develop further than thirty-two cells where the 

 pressure was greatest. 



Experiment 3.— Arbacia eggs five minutes after fertilization were 

 shaken violently for about a minute. The membranes suri-ounding the 

 eggs were thereby broken: the eggs were then placed in artificial sea 

 water in which there was no calcium. Eggs were thus ti'eated at two- 

 celled, four-celled and eight-celled, with the following results: 



