SPINAL CORD REGENERATION. I 473 
The severed ends of the spinal cord have become slightly 
rounded off and the canalis centralis, opened by the cut, has been 
closed over on both sides of the wound. This has apparently 
been effected by a rearrangement of the existing cells. No karyo- 
kinetic figures have been observed in this region. As yet, no 
nerves have grown out from the ends of the cord nor can their 
beginning development inside it be noted in this region. The 
motor roots of the spinal nerves have, however, made their 
appearance. 
The ends of the notochord also have become rounded off, 
except in the two cases noted above. ‘The proliferation of con-' 
nective tissue from the notochordal sheath has begun and with 
the mesenchyme forms a fibrous mass attached to the epidermal 
ingrowth. The yolk has in each case formed a slight mound 
just below the site of the wound, caused by the diminution in 
its surface tension at this point at the time of operation. 
This stage represents the period of primary repair and prep- 
aration for the active regeneration which begins shortly after. 
Embryos 2 days after operation. The embryos at this time 
measured from 4.5 to 6 mm. in length and possessed branched 
gills. The cleft in the back of the animals was largely limited 
to the dorsal fin. All the embryos moved voluntarily by repeat- 
edly turning the head from side to side No spontaneous move- 
ment-was observed in the hinder end of the body. A few embryos 
exhibited a very imperfect type of locomotion. This was pro- 
duced by an. increase in the number and force of the side to side 
motions of the head which caused a swaying of the tail. Though 
at first purely passive, the tail muscles were excited to contraction 
with the continuance of the head movements. The locomotion 
which resulted from their action carried the embryo over short 
distances. The lack of synchrony between the two nervously 
isolated portions of the body prevented an efficient swimming 
motion. As soon as the head end became quiet, the tail move- 
ments diminished in force and ceased. 
Gentle tactile stimulation of the anterior end of the body 
resulted in responses only from that end. Long continued 
stimulation of the region in front of the cut produced swimming 
THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 25, NO. 5 
