160 H. SAXTON BURR 



themselves. In the first place, it has been shown (Burr, '16) 

 that the absence of a peripheral end-organ prevents the growth 

 period in that portion of the central nervous system with which 

 it is normally connected. This suggests that functional activity 

 is the factor, or, in other words, that the passage of olfactory 

 stimuli along the olfactory nerve serves to complete the develop- 

 ment of the cerebral hemisphere. In addition to the above, it 

 may be that it is necessary for the complete growth of the hemi- 

 sphere that there be a pathway of discharge for the stimuli as 

 well as a system by which stimuli may be received. In the 

 second place, it is possible that functional activity does not enter 

 into the problem at all, for it may be that the neurones of the 

 cerebral hemisphere complete their development as a result of 

 the ingrowth of the olfactory nerve regardless of the transmission 

 of olfactory stimuli, the mere fact of the connecting up of the 

 telodendria of the primary olfactory neurones with those of the 

 secondary neurones serving as the factor necessary for the further 

 growth of the hemisphere. 



With the object of finding some data as to which of the above 

 factors is operative, a number of experiments were performed 

 on Amblystoma larvae in the spring of 1917, and repeated in the 

 spring of 1919. Three types of experiments were carried out. 

 In the first, the right cerebral hemisphere and the right nasal 

 placode were transplanted to the region just posterior to the 

 right limb so that the nasal placode was buried beneath the 

 epidermis. In the second, the same structures were transplanted 

 in the same way except that in this instance the olfactory epithe- 

 lium was healed into the skin on the surface with the telencephalon 

 deep in the tissue beneath it, maintaining in so far as possible 

 the same relation between hemisphere and placode as exists in 

 the normal position. In the third, a thin block of celloidin or of 

 paraffin was healed into a cut made across the junction of the 

 diencephalon and the telencephalon on the right side. These 

 experiments created the following conditions: 



In series I the nasal placode was healed in beneath the epi- 

 dermis, thus preventing functional activity of the end-organ. 

 Since in series II the nasal placode was healed in at the surface 



