Analysis of Rate of Regeneration 407 
chord. The wall of the new notochord like that of the old is 
formed by connective tissue which is deposited in concentric 
layers. (3) The fibrous connective tissue that fills the fins of 
the new tail comes from the descendents of fiber forming cells 
present in the old tail—. e., the fiber forming cells of the old 
connective tissue multiply, giving rise to masses of undifferen- 
tiated cells which are seen in the early stagesof regeneration. 
Later these cells differentiate into the connective tissue of the 
new tail. ‘The connective tissue in the fin and around the noto- 
chord seem to be of similar origin. (4) The muscles appear rela- 
tively late in the development of the new tail. The partially 
undifferentiated cells, sarcoblasts, that develop into new muscle 
fibers are described by Barfurth as coming from the muscle 
fibers of the old tail that are near the level of injury. (5) The 
new nerve cord is an outgrowth of the old. It regenerates more 
rapidly than the notochord or muscles. 
Jt is interesting to note that in all the tails sectioned the old 
notochord projects a short distance into the new tissue of the 
regenerating tail. The changes due to differentiation in each 
state of development represented by a measurement of the regen- 
erations of the operated series in Experiment IV, are shown in 
the following chart. The regions referred to in the chart are 
represented diagrammatically in Fig. 6. 
DISCUSSION OF DATA 
Before entering upon a discussion of the data presented by the 
operated series of these experiments it is to be observed that the 
tadpoles in the control series did not grow during the experi- 
ment. ‘able II includes the record of the control series during 
the course of Experiment II. Since the animals were not grow- 
ing, any increase in length noticed in the operated series was due 
to the regeneration of the part of the tail removed by the operation. 
The foregoing data show that in each series operated upon the 
rate of regeneration immediately after the operation is slow; it 
then increases rapidly until the maximum is reached, then 
decreases rapidly at first but gradually more and more slowly. 
