386 THE FURTHER DIFFERENTIATION OF THE 



and first two spinal segments from another embryo are grafted 

 (fig. 187), there will be two medullas, and an increased number of 

 fibres in the descending tracts as compared with the normal. The 

 result is an increase in the number of motor neurons in the ventral 



1.0 \ MEDULLA 



272 



1.0 



1.0 



Weight 

 Patios 



Case 

 ERL8 



0.90 



0.80 



0.56 



0.47 



0.40 



0.34 



0.28 



Cell 

 Ratios 



0.74 



0.92 



0.77 



0.40 



0.31 



Weight 

 Ratios 



MEDULLA, 

 233 



156 



Trans- 

 plsuited 



Medulla 



180 



TrSSl 

 277 



TrSS2 

 243 



SS6 

 113 



SS7 

 90 



Case 

 TrBrSc 1 



1.0 



0.65 



0.77 



1.15 



1.04 



0.48 



0.38 



Cell 

 Ratios 



Fig. 187 

 Diagram showing the number of cells in various regions of the medulla and spinal 

 cord of Ambly stoma in a normal embryo (case ERL8) and in an embryo from 

 which spinal segments 1-5 were removed and replaced by an extra medulla and 

 spinal segments i and 2. SSi, SS2, etc., spinal segments i, 2, etc. TrSSi,2, 

 grafted spinal segments 1,2. The figures within each segment represent the 

 average number of cells seen in a transverse section. The weight ratios are 

 estimated from the weights of reconstructed wax models of the various regions. 

 (From Detwiler, Quart. Rev. Biol, i, 1926.) 



