THE EFFECTS OF THE REMOVAL OF THE NASAL 

 PITS IN AMBLYSTOMA EMBRYOS 



HAROLD SAXTON BURR 



From, the Oshorn Zoological Laboratory, Yale University 



FOURTEEN FIGURES (THREE PLATES) 



INTRODUCTION 



Many of the difficulties encountered in the study of the nervoua 

 system by the usual methods are obviated by experiments upon 

 embryonic material in which nerve fibers are not yet developed 

 and the blood has not begun to circulate. In this way it is 

 possible to observe the effect of the removal of an end organ 

 upon the central nervous system without undue complication of 

 the factors involved, and furthermore such a method makes 

 possible the study of the formative influence one part may exert 

 on another during ontogeny. 



The number of investigators who have applied this method 

 is relatively small. 



In 1906 Braus extirpated the forelimbs of the larvae of Bombi- 

 nator before the outgrowth of the brachial plexus, with a view 

 to determining the effect of the absence of the limb on the ventral 

 horn of the spinal cord at the level of the brachial plexus. The 

 experiment showed that there was at first no observable effect 

 on the cord. The brachial nerves grew out into the surrounding 

 tissue and ended more or less blindly. The size and number of 

 the motor cells of the ventral horn was in no distinguishable 

 manner changed. But this investigator found that when the 

 operated larvae were kept alive until just before metamorphosis 

 and then killed, a distinct reduction in the size of the cells of 

 the ventral horn was discernible. Hence, he concluded, as a 

 corollary to the theory proposed by Roux in 1885, that the devel- 

 opment of the central nervous system was readily divisible into 



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THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 20, NO. 2 

 FEBRUARY, 1916 



