313 



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8) Kingsbury, The Structure and Morphology of the Oblongata in 

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Nachdruck verboten. 



The Dispensibility of GrraTity in the Derelopment of the 



Toad's Egg. 



By T. H. Morgan. 

 The experiments of Roux i), on the development of the frog's egg 

 placed on a slowly rotating wheel, seemed to show that gravity as a 

 factor acting in a definite plane is not necessary for the development 

 of this egg. The suitability of the experiment to settle this point has, 

 however, been questioned by several recent writers. The experiment 

 of Katheriner2) seemed also to lead to the same conclusion as had 

 that of Roux ; but Moszkowski ^) in a very recent paper has attempted 

 to show that the influence of gravity, if it extends over the first half- 

 hour after fertilization of the egg, suffices to determine the bilaterality 

 of the embryo. Since Katherinek appears to have allowed the eggs 

 he used to remain quietly for half an hour of the fertilization he did 

 not, Moszkowski claims, really exclude gravity as a factor in the 

 development. In the light of Moszkowski's statements this criticism 

 seems well taken, so that it remains a point of capital importance to 

 determine if the frog's egg can develop if at no moment after being 

 removed from the uterus gravity is allowed to act on it in a constant 

 direction. The following experiment has given a decisive answer to 

 this question so far as the toad's egg is concerned. 



1) Roux, Archiv f. mikr. Anat., Bd. 29, 1887. 



2) Katheriner, Archiv f. Entwick.-Mech., Bd. 12, 1901 



3) Moszkowski, Archiv f. mikr. Anat., Bd. 60, 1902. 



