CHART I 
ECTODERM 
3 days* (Three irregular layers of Lacking. 
cubical cells with mitotic’ 
figures. 
sdays Three layersmore regular. A solid rod of round cells. 
The outer one relatively 
thinner, of somewhat flat- 
tened cells. 
7 days Three layers distinct, cells of/Larger, somewhat reticular. 
the outermost flat, those) Wall very thin, composed 
of the innermost columnar.| of two or three layers of| 
connective tissue in which! 
nucleated cells are still 
persistent. 
The sameasatsevendays. (Core an open reticulum with| 
1o days 
lining the wall. Wall 
thicker and without nu- 
cleated cells. 3-5 layers| 
of connective tissue, with| 
nuclei, drawn very closely; 
around the wall. 
Middle layer less evident. |Core unchanged. The wall, 
12 days ‘The inner and outer layers| thicker. 3-5 layers of 
quite regular. connective tissue still bear- 
ing nuclei are drawn very, 
closely around the outside 
of the wall and seem in 
process of being added in 
concentric layers to the) 
wall. 
14 days The same as at twelve days.\Changes observed for 12 
NOTOCHORD 
nucleated cells in a layerjRelatively smaller. 
NEURAL TUBE 
Extending halfway to the tip 
of the regenerating tail. 
Relatively large. 
Same as three days. 
Not different in structure! 
but relatively much longer. 
No evident change. 
Dorsal aorta definable, 
= 
MUSCULAR TISSUE REGION 
Specialized cells lacking. 
regions. 
injury. 
region. 
cle fibers that take an eosin! 
stain, and are grouped 
like the fibers of the old 
Many 
muscles. 
the developing-fibers. 
days are continued. 
No change in neural tube. 
Dorsal aorta with a thicker 
wall. 
No change in neural tube. 
Dorsal aorta extending rela-| 
tively nearer the tip of the 
new tail. 
groups of fibers appearing. 
Changes observed upon the 
twelfth day are continued. 
Muscle region occupied by] 
cells observed in the fin! 
A layer of sarcoblasts under, 
the ectoderm in the muscle| 
Many of the sarcoblasts dif- 
ferentiated into small mus- 
sarco- 
blasts still present among: 
Muscle fibers larger; new 
FIN REGION 
Filled with closely packed 
round or cubical cells with 
large nuclei. No tissue 
of fibrous appearance 
[nO ED ns Se tee 7 er 
‘Muscle fibers absent; a veryNot a solid mass of cells as 
few small sarcoblasts on! 
and very near the level of 
before. Some cells with 
fibrous outgrowth. Cells 
with large nuclei. 
_—$—$<<— 
Fins filled with loose fibrous 
tissue. Nuclei few ex- 
cept between the muscle 
regions. 
Very fibrous tissue through- 
out. Nuclei few except in 
region of the notochord. 
Connective tissue between 
the muscle regions form- 
ing a vertical partition. 
The same changes noted on 
the tenth day continue. 
No evident change in struc- 
ture since the twelfth day. 
correspond horizontally with the number of days after operation named in the column to the left. 
EXPLANATION OF CHART 
The changes in state of differentiation of ectoderm, notochord, neural tube, muscle tissue, and connective tissue are written in vertical columns and 
