OCTOPUS ARM, REGENERATION AND STRUCTURE 7 
placed a piece of filter-paper on the wound immediately after 
the operation had been performed. I could not detect any 
moisture on the paper. ‘This retention of the blood after amputa- 
tion is in all probability associated with the ability of the arm to 
cast off distal portions by means of autotomy. According to 
EKisig and Riggenbach, Octopus de Filipi frequently casts off 
the greater portion of several tentacles in this manner. Riggen- 
bach also mentions the ability of the octopodes to free their dis- 
tally held arms by simply casting off the held portion. TI also 
observed similar cases of autotomy of the arm of Octopus vulgaris, 
but I believe that the ability to autotomize is confined to the 
distal portion. I was not able to find any portion of the 
arm which was modified or in any way arranged for autotomy. 
Neither do any of the numerous publications treating of the 
structure of the arm mention the presence of any mechanism 
especially adapted to autotomy. (It is a well-known fact that 
many arthropods are provided with such mechanisms.) Gener- 
ally four-fifths of the arm is cast off. But this is not always the 
case, and the distance between the base of the tentacle and the 
point of rupture is by no means always the same. Riggenbach 
mentions some cases where this distance averages about 2 cm., 
sometimes more, sometimes less. 
Immediately after operation the external rim of the wound 
contracts spasmodically; this contraction is especially noticeable 
in the dermis. The external parts of the wound are thus covered, 
but the central musculature and the axial nerve remain unpro- 
tected. The axial nerve even protrudes beyond the surrounding 
tissues. Figure 5 shows a wound about one and a half hours 
after operation. The protrusion of the axial nerve is quite 
obvious. With the help of a magnifying glass I was able to see 
the myelin cords, the central nerve-fiber mass, and even the 
main artery quite plainly. This fact shows that this part of 
the wound was still without any covering whatever. Figure 6, 
showing a later stage (about ten hours after operation), presents 
quite a different picture. The dermis has contracted more 
closely over the wound, but has not succeeded in covering it 
completely. The axial nerve no longer extends beyond the 
