476 DAVENPORT HOOKER 
with the growth of the embryo as a whole. In consequence, its 
cut ends have been drawn away from each other in the preceding 
24 hours development. As the initial separation of the two pieces 
of the cord is different in each embryo, dependent on the gaping 
of the wound after operation, a comparison of the distance be- 
tween their cut surfaces in the different stages gives no valid 
results. The position of the developing spinal ganglia in relation 
to the ends of the cord does, however, offer a criterion by which 
this may be demonstrated. In this stage the ganglionic anlagen 
in the anterior two-thirds of the body have become separated 
from the cord and lie in more intimate connection with the myo- 
tomes than with it. The distance between the most caudad gan- 
glion anlage in front of the cut and the end of the anterior portion 
- of the cord added to that between the cut surface of the posterior 
portion and the first ganglion anlage caudad to it is less than 
between any two ganglia of one side. As no degeneration of 
the cord has taken place at its cut surfaces, its retraction past 
the ganglionic anlagen as fixed points seems to be the only valid 
. explanation of the shortening that has occurred. 
The 48 hour stage marks the first step in the establishment 
of the primary reunion between the two pieces of the spinal cord. 
It is characterized by a procedure of the same nature as that 
seen in the development of the peripheral nerves, namely, the 
outgrowth of motor nerve fibers. In this case, however, they 
grow out from the ends (descending and ascending processes) 
rather than from the sides (collateral processes of Coghill) of the 
cord. 
Larvae 4 days after operation. Four days after operation the 
larvae measured from 6 to 7.2 mm. in length. The body had 
begun to assume the rounded, tadpole form due to the rapidly 
progressing absorption of the yolk. The external gills were well 
developed and the tail fins had become transparent. The only 
external mark of the operation was a nick in the dorsal fin which 
extended down to, but not into, the body. All the tadpoles were 
active and swam voluntarily. Tactile stimulation of either end 
of the body caused the larvae to swim. In the majority of cases 
the swimming movements, though not entirely normal, were 
' 
