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Aufsätze. 



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Half-Embryos and Whole-Embryos from one of the first two 

 Elastomeres of the Frog's Egg. 



By T. H. MoBGAN. 



Roux, and subsequently Hertwig, have made the experiment of 

 killing with a heated needle one of the first two blastomeres of the 

 frog's egg, and have reached diametrically opposite conclusions as to 

 the result. 



Neither author has apparently taken into consideration the position 

 subsequently taken by the uninjured cell, and the resulting difference 

 in the cleavage. It is the object of this paper to point out that 

 this oversight may have lead to the difference in the results. 



Born showed in 1884 that if the egg prior to its cleavage be 

 fixed with the white pole turned upwards, the contents of the egg, 

 owing to the differences in the specific gravity of the parts, slowly 

 rotates so that a new arrangement of the contents is brought about. 

 There is every reason to believe that a similar rotation takes place 

 if the egg is reversed after the two-cell-stage, 



O. ScHULTZE has recently shown that if at the two-cell-stage 

 the frog's egg be turned with the white pole upwards then each 

 blastomere will give rise to an embryo of half the normal size. 



It seemed to me that these results of Schultze showed that the 

 difference in the results of Roux and Hertwig was owing to the 

 difference in the positions taken by the living blastomere after the 

 operation. This led me to made a series of experiments to test the 

 hypothesis that I had formed. 



Method. 

 Roux has given in the Anatomischer Anzeiger a detailed state- 

 ment of the best method of treatment of the eggs of the frog after 

 removal from the uterus. In general I have followed these directions, 

 the principal difference consisted in turning some of the eggs after 

 the operation so that the white pole was upwards. Owing to the 

 fact, that the membrane was pierced, and a large or small extra-ovate 

 protruded through it, the egg could easily be turned into any desired 



