OCTOPUS ARM, REGENERATION AND STRUCTURE 13 
on the contrary the very first sucker to be formed in the course 
of regeneration. Three or four weeks after operation, the first 
chromatophores appear in the regenerated part. They are 
lighter in color than the chromatophores of the arm stump. 
Figures 15 and 16 show regenerated pieces in an advanced stage 
of development. The only differences between the stump and 
the regenerated part consist in the different thickness and the 
different coloring of the chromatophores. 
The arm of Eledone regenerates in the same way as the arm 
of Octopus vulgaris, with the exception that the suckers remain 
arranged in single file; this beg their normal and permanent 
position. 
I did not study the regeneration of the arm of the Decapoda 
very closely. JI was able to observe the complete healing of the 
wound and the formation of a dome-shaped regeneration knob,? 
but not able to follow up the development of the suckers, as 
the animals generally died before they reached this stage. Brock 
claims that the arms of the decapodes lack all ability to regen- 
erate. As the arms of the decapodes are considerably shorter 
than the octopus arms, they are not subject to such frequent 
injuries. Nevertheless, the Decapoda are able to replace a lost 
arm; only the manner in which they do so differs from the way 
in which the octopus repairs the same damage. Doctor Naef 
showed me a sepia (at Naples) which had lost almost a whole 
arm. The animal had already begun to replace the lost part, 
but not by means of regeneration from the old stump, but by 
developing that rudimentary buccal arm’ which was correlated 
to the lost arm. ‘This arm developed from a rudiment had the 
same structure as a normal arm and differed from the latter only 
* The regeneration knob of the sepia arm is centrally located, whereas the 
knob of the Octopus vulgaris is nearer the exterior side. No lash-like append- 
age or thin process is developed. The difference in thickness between the stump 
and the regenerated part is not so great. Perhaps the different arrangement 
and location of the myelin cords is the cause of this. 
’ The buccal funnel of the decapods is a set of rudimentary arms and corre- 
sponds to the inner circle of arms of the Nautilidae. The buccal funnel of the 
decapods possesses seven to ten rudimentary arms, which, according to Naef, 
are provided with two rows of suckers. 
