24 MATHILDE M. LANGE 
and one nucleolus. They migrate to the distal portion of the 
wound, and in combination with the neuroblasts form the second 
blastema (fig. 31). They multiply very rapidly by means of 
mitosis (fig. 32). About twelve to fourteen days after operation 
the sarcoblasts of the proximal portion of the regenerated piece 
begin to transform into the definitive muscle fibers. But this 
differentiation does not begin simultaneously in every part of 
the musculature. The longitudinal muscles are the first to begin 
this process, and in these the very first differentiation takes 
place in those parts which are nearest to the perimuscular con- 
nective-tissue membrane. The differentiation progresses distal- 
ward in the longitudinal muscles. The transformation of the 
transverse muscles into their final form probably takes more 
time, for they are still in the sarcoblast stage at a time when 
the surrounding longitudinal muscles already appear as quite 
well-developed muscle cells. Most likely this is due to the differ- 
ent intensity of growth in the different muscle fibers. The 
muscle fiber can only grow by means of sarcoblasts. The best 
proof of this assertion is the fact that at the distal end of every 
regenerated piece as well as of every normal arm there are no 
muscle cells, but only sarcoblasts. As the difference in thickness 
between the regenerated piece and the stump is particularly 
great at the juncture of these two parts, there must be an active 
and intense growth in breadth at this point, in order to equalize 
this difference in thickness. The transverse musculature will 
probably take an active part in this growth. Whereas in the 
longitudinal muscles the point of active and intense growth is 
always carried farther and farther away from the juncture the 
more the regenerated piece grows in length, the transverse 
muscles of this part remain in a stage of active and intense 
growth for a much longer time. Hence the transformation of 
the sarcoblasts into muscle fibers begins later in the transverse 
muscles than in the longitudinal muscles. That the sarcoblasts 
of the Cephalopoda are a product of the old muscle fibers has 
already been mentioned. This is a case of new formation from 
preexisting tissue and verifies the statement that a new tissue 
can only be formed by the same kind of old tissue. According 
