89 
1914-15.] Eegeneration of the Legs of Decapods. 
short, the fibres show signs of stretching. There is much plasma now 
present in spaces between the muscle-bundles, and this covers the larger 
part of the surface shown in section. The vessel and nerve, also much 
stretched, have the same relative positions as they had in the papilla, 
but the new diaphragm is changed. The upper flap, which before ran 
parallel to the epidermis of the stump, is now turned down towards the 
nerve, and its lower part forms a portion of the funnel-like sheath 
before mentioned. 
From these appearances we may conclude that the following has 
happened : — Release of the papilla from its envelope exposes a surface 
less resistant to the blood-pressure than that of any other part of the 
body. The result, of course, is that expansion of the epidermis takes 
place forthwith, and the layer previously several cells thick is now reduced 
to one cell in thickness. Another factor may help in the process, and this 
is the change taking place at the diaphragm. The dorsal free flap was 
seen before moulting to be lying parallel to the epidermis and leaving a 
considerable space for the return of venous blood between it and the nerve. 
When the papilla loses its tough envelope, the great difference in pressure 
between the blood within and the surrounding medium causes this part 
of the diaphragm to be forced against the nerve, so preventing the return 
of venous blood. The thick-walled artery, however, containing fluid at 
a still higher pressure, continues to pump its blood into the limb-cavity, 
and thus swelling out occurs till the much-folded epidermis has become 
sufficiently tense to raise the pressure within the new leg and cause partial 
opening of the valve, so establishing a return of the venous blood. This 
probably would only take a minute to happen, and this time corresponds 
with what is actually occupied in enlargement at the moult. 
To confirm the above I took a crab ready for moulting, with papillae 
fully formed. By careful dissection the envelope was removed without 
much damage to the epidermis, and at once the leg assumed the size in 
which it is found immediately after moulting. 
Discussioj^. 
In the above descriptive account several points are worthy of discussion. 
The first of these is the outward form of the papilla. 
The formation of a papilla is itself a beautiful adaptation to the 
requirements of these higher decapods. In other animal groups where 
regeneration of the appendages or parts of the body takes place, the growth 
is graded in time till a more or less complete part is formed. Examples 
of such a process are seen in the regenerating ray of a starfish or in larval 
