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position and it would hold this position, in most cases, until the 

 subsequent cleavages had taken place. The eggs after the operation 

 were placed on a piece of moistened glass, and kept for ten hours 

 under a bell -jar in a saturated atmosphere. Afterwards they were 

 placed in a dish of water where the subsequent development took place. 



If, immediately after the operation, the eggs be simply thrown into 

 a dish of water they assume all possible positions with respect to the 

 vertical and tend to hold that position through the subsequent deve- 

 lopment. 



Although Roux has not made any definite statement in regard 

 to the position of the eggs, which he studied yet it is probable, judging 

 from his methods, that in all cases after the operation the black pole 

 was turned upwards. This is of importance when we consider his 

 results. 



Hertwig also has made no statement as to the position of the 

 eggs in his experiments. He says that in the later stages the dead 

 or injured half was down and the living part above ; but the essential 

 thing is to know what position the eggs took immediatly after the 



operation. 



Results. 



The following description applies to those eggs of Rana esculenta 

 which had been kept on a glass plate, in a moist chamber, after the 

 operation. The cleavage of these eggs was studied during the sub- 

 sequent two or three divisions. This is all important because as 

 Hertwig has shown the injured cell may also divide, showing that 

 the nucleus was not destroyed or even injured by the operation. 

 Such eggs were of course removed. 



In all I have operated on 155 eggs and from these I got 8 em- 

 bryos. The larger number of these eggs had the white pole turned 

 upwards, but only a very small number of these developed embryos. 

 I have only two good embryos from these eggs. Although a smaller 

 number of eggs were placed with the black pole upwards yet a much 

 larger number of good embryos were obtained viz six. 



The results of these experiments may be briefly stated. 



From those eggs with the black pole turned upwards I got six 

 half embryos, i. e. embryos having only the right or left side of the 

 body developed. These embryos are in every respect like those de- 

 scribed by Roux. They have only the half medullary fold present 

 or anteriorly a little more than half present. 



In some of those eggs with the white pole turned upwards 

 the third horizontal cleavage appeared nearer the upper pole so that 



