166 H. SAXTON BURR 



to indicate that the cell bodies migrate or are drawn caudally 

 in the process of development. That this is not so I hope to 

 show in a paper to be published later. Rather, in the process 

 of differentiation, it is the glomeruli that move through the growth 

 of the dendrites of the secondary neurones. When the nasal 

 placode is removed the secondary olfactory neurones develop 

 during the first phase of nervous differentiation. Failing, then, 

 to make connections with the telodendria of their receptors, the 

 growth phase does not ensue. When the placode is present, 

 connection is established and further development follows. 



In a previous paper (Burr, '16 a) the statement was made that 

 "the presence of the latter (nasal placode) acts as a stimulus to 

 the regeneration of a new telencephalon through the ingrowth 

 of the olfactory nerve." The present experiments indicate the 

 olfactory neurones can stimulate not only regeneration, but can 

 also carry through the second or growth phase of nervous 

 development. 



As a secondary aspect of the operation it was noted that the 

 transplants in every case showed a healthy development. The 

 size of the transplant was in the main comparable to the normal. 

 For instance, measurements made of a normal telencephalon 

 showed an anteroposterior length of 740 ju; of a series I, 1080 ju, 

 and of a series II, 800 m- Evidently then, the hemisphere, though 

 removed from its normal blood supply, was able nevertheless to 

 obtain the materials necessary for growth. Under normal sur- 

 roundings, the hemisphere is supplied with blood from two 

 sources; first, the blood-vessels of the pia mater, and, second, 

 the modification of the pia and ependymal wall, the choroid 

 plexus. When the telencephalon is transplanted apparently the 

 anlage of the pia is transferred also, and hence we find pia blood- 

 vessels penetrating the brain substance. The derivation of these 

 blood-vessels is any adjacent arteriole or series of arterioles. 

 When an arteriole of sufficient size comes into contact with the 

 thin membranous wall that forms the medial boundary of the 

 transplanted hemisphere in the region that normally gives rise 

 to the choroid plexus, we find such a plexus formed (figs. 6 

 and 9). 



