438 DAVENPORT HOOKER 
taneous movement for the first time. This is from two and a 
half to three days after operation. The 8 reaction, which is of 
course the most primitive manifestation of the swimming move- 
ment, rapidly passes over into a period in which active locomo- 
tion is produced. In these embryos with the reversed spinal 
cord the first movements producing locomotion are ill coor- 
dinated and the consequent movement of the embryos is far 
from normal. As a rule spontaneous movement on the part 
of these operated embryos takes the form of the double C reac- 
tion for a considerable period after locomotion may be pro- 
duced as a result of stimulation. From a careful study of the 
movements of these embryos with reversed middle piece it is 
evident that there is little or no coordination between the por- 
tions and that locomotion is produced by the activity of the 
central (reversed) portion of the body which drags the rest of the 
organism into activity. It is true that, during these movements 
which produce locomotion, both head and tail portions of the 
embryos do move by the contraction of the myotomes situated 
in them, but there is every indication that the stimulation of 
these myotomes in the head and tail is brought about directly 
through the pull of the skin over them which is caused by the 
movements of the middle piece. In a previous paper (711) I 
demonstrated that very slight tension on the skin of an embryo 
produced by pressure at a distant point is capable of mechani- 
cally stimulating the myotomes to activity. The cause of the 
movements in these embryos is apparently identical with that 
described in Paper I of this series. 
From this time on the embryos show a steadily increasing 
sensitivity to tactile stimulation and a steadily increasing 
amount of coordination in the responses. As soon as even the 
most primitive type of coordination was exhibited in the reac- 
tions to tactile stimulation, the embryos began to show spon- 
taneous swimming movements, which with the passage of time 
gradually improved until five to six days after operation many 
of the embryos were almost, if not entirely, normal in their 
movements. Indeed in several cases it was only possible to 
differentiate the operated embryos from their normal controls 
