88 
Proceedings of the Royal Society of Edinburgh. [Sess. 
by a layer of muscle-corpuscles. Outside these is a sarcolemma 
of connective tissue with few nuclei. Everything is compact, 
and there is very little space left within the papilla. 
The hermit crab has a papilla which, on maturing, is found to be 
curved. It is smaller in proportion to the post-exuviate size 
than that of the lobster, but the epidermis and muscle present 
the same appearances, being several cells thick, and striated, 
respectively. 
In the crab, papilla formation is most perfect, and in the case of 
walking legs the new member is folded on itself three times 
inside a tough, chitinous envelope. The epidermis, again, is 
composed of several layers of cells, and the muscle-fibres in it 
are striated like those in the normal leg, with Dobie’s lines 
visible. The outer wall of the papilla has pigment, but no 
calcareous deposit. 
3. The Changes at Moulting . — I have only once seen the act of 
moulting taking place, and that was in the case of a shore crab. 
The process has been seen before in a large decapod (17), but no one 
has recorded a case of moulting in which a papilla enlarged to form 
a normal leg. The crab was fixed within ten minutes (fig. 16), and 
shows the shell with its empty papilla-envelopes, and the new legs 
on the crab itself. The carapace split along its posterior margin, 
and one after another the legs were withdrawn. What surprised 
me very much was that the new legs were drawn out of the old shell 
exactly as they are in the photograph, i.e. about normal size. There 
was no gradual swelling or blowing out. Whereas the other legs were 
velvety to the touch, normally pigmented, and functional, the new ones 
were pale in colour, waving about in the currents created by other limb- 
and body-movements, and absolutely devoid of spontaneous movement. 
I had previously considered, like other observers, that the great increase 
in size would take a few hours to occur, as I had not previously seen 
a crab nearer the actual moulting time than at most three hours, but 
my fortunate experience proved to me conclusively that increase is 
immediate. 
The examination of serial sections of the newly expanded limbs shows 
exactly what has happened. The epidermis is now composed of a single 
layer of columnar cells. Muscle-fibres are attached to this and stretched 
between the tendon-plates before mentioned and the wall of the limb. 
They are much thinner than those seen in a mature papilla, and the 
nuclei are not so plentifully scattered beneath the sarcolemma. In 
