44 HAROLD SAXTON BURR 



The suggestion is made here that it would be possible by very 

 careful operating to remove the nasal analge without disturbing 

 the duct rudiment, and vice-v^ersa. The material at hand rather 

 indicates that the duct is derived not from the surface epithelium 

 but from the cells of the nasal sac. The above operations would 

 make it possible to arrive at a definite conclusion experimentally 

 so far as Amblystoma is concerned as to the exact origin of the 

 duct. 



///. The Brain 



Owing to the difficulties encountered in keeping noseless larvae 

 alive up to metamorphosis, the report on the effect of the absence 

 of the olfactory organ on the fiber tracts of the forebrain must 

 be postponed until later. The effect on the gross morpholog}' 

 can, however, be given in its entirety at this time. For the 

 sake of clarity the description of the brain of the six months old 

 larvae will be given first, since, as will be shown, the effect of the 

 removal is not immediate. 



Figure 7 will make evident at once the effect of the absence 

 of the nasal sac on the gross morphology of the telencephalon. 

 The hemisphere of the operated side is markedly smaller than 

 that of the unoperated. This reduction in size, however, is 

 related largely to the anterior portion of the telencephalon. In 

 other words, the olfactory bulb as such is greatly reduced in 

 size — a reduction which is apparent also for some distance cau- 

 dally. In the region of the primitive hippocampus, on the other 

 hand, the two hemispheres are equal, barring slight imevenness 

 in the sections (text figures 1, 2 and 3). 



A study of the cross sections of brains of operated larvae show 

 quite as strikingly the above facts. Figure 12 through the ol- 

 factory bulb of the unoperated side shows no sign of the hemi- 

 sphere of the operated side. Figure 14 from a section some 

 170 )u caudad shows the right is greatly reduced in size. A sec- 

 tion still further caudad at the level of the interventricular fora- 

 men shows no distinguishable differences in the two hemispheres 

 other than that in the size of the ventricles. A comparison of 



