OCTOPUS ARM, REGENERATION AND STRUCTURE 11 
in figure 11. All suckers are at first formed in the shape of little 
transverse folds arranged in single file. Later they are rounded 
off to little papillae. This process of rounding off seems to start 
in the center and progress sideward, so that the papillae are in 
quite a different position from the original folds. The latter 
were quite centrally located, whereas the papillae or warts have 
a lateral position. As the folds are rounded off alternately, 
once to the right and once to the left, the double row of suckers 
characteristic of the arm of Octopus vulgaris is thus gradually 
formed. But the above is only true of the suckers, which origi- 
nate in the regenerated process. Attention has already been 
drawn to the fact that the regenerated process is attached to the 
external half of the arm. The process is considerably thinner 
than the stump of the arm, and in comparison to it looks like 
a thin lash-like appendage. Therefore, a considerable portion 
of the obtuse end of the stump remains free. On this free end 
the first regenerated suckers are formed in the shape of little 
transverse folds, but their further development differs somewhat 
from the development of the suckers located in the regenerated 
process. While the final double-rowed arrangement of the latter 
is already visible at an early stage of their development, the 
suckers of the free end remain arranged in single file till they 
are a great deal further advanced, and some of them even remain 
so permanently. The above is very well illustrated in figures 
13 and 14. The four proximal suckers are arranged in single 
file and already show the invagination, which eventually leads 
to the formation of the sucking cavity and the adhesive part. 
Above these four suckers are ten to eleven newly formed suckers 
belonging to the regenerated process. ‘These still show the form 
of papillae and are not nearly as well developed as the lower 
four, but their position already indicates their final arrangement 
in two rows. Above these papillae we can detect two to three 
small transverse folds arranged in single file. The latter are 
suckers at a very early stage of development. 
How does the regeneration of the arm compare with its normal 
development? The arm of the octopus embryo can be divided 
into two parts—a rather thick proximal part, provided with 
THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 31, NO. lL 
