PLATE 4 
EXPLANATION OF FIGURES 
7 Five-day chick embryo. Section through anterior thoracic segment 
(X 60), showing small primordia of sympathetic trunks (sy) in the absence of 
spinal nerves and neural tube. 
8 Embryo of frog, no. 9, three and one-half days after operation. Section 
(X 275) showing ventral nerve-root (vr) accompanied by cells of medullary ori- 
gin (mc) in absence of spinal ganglion and dorsal nerve-root; J, line along which 
cut surfaces of neural tubes of two embryos healed together. 
9 Embryo of frog, no.6, three days after operation. Section (X 365) showing 
ventral nerve-root (vr) accompanied by cells of medullary origin (mc) in absence 
of spinal ganglion and dorsal nerve-root. 
34 
