85 
1914-15.] Regeneration of the Legs of Decapods. 
formation of a new valvular diaphragm exactly the same in type and 
origin as that which has so recently saved the blood of the animal, and 
which now, with disintegrating blood corpuscles adhering to it, is still 
covering the new proliferating layer. Epiderm cells at the edge of the 
stump are sending processes across the limb-cavity which fuse. Only a 
few nuclei are seen, and the whole mass is plicated as if allowance were 
being made for expansion. 
On the twelfth day this new diaphragm is almost completely formed. 
It then consists of a wavy band of clear material with a definite outer and 
inner border. From the ventral side of the limb it arises from epiderm 
cells there, and passes upwards towards the nerve. Reaching this structure 
it turns inward along its course and takes part in the funnel formation 
before mentioned. On the dorsal side the cell processes do not run down 
to the nerve, but form a layer covering the more central epiderm of the 
stump, and thus running parallel to but at some distance from the nerve, 
form the upper part of the funnel (fig. 7). The functional significance 
of this layer will be discussed later. 
It is perhaps of importance to note at this point that a new diaphragm, 
the possession of which is necessary for the continued safety of the crab, 
is the first structure to be laid down. Haseman (10), writing on direction 
of differentiation in regenerating appendages of crustaceans, maintains that 
in the cheliped of the hermit crab the distal portion is the first to be laid 
down and differentiated. He says that since the claw portion is the most 
important part of the leg, it is probably on this account that it is re-formed 
first in the new appendage. The observations made were macroscopic 
only, and therefore Haseman has come to a conclusion which the facts at 
present stated refute. The cheliped of the hermit crab, like the other legs, 
is differentiated from the base outwards, and the process begins at the new 
diaphragm. 
When the single layer of epidermis proliferated over the stump is com- 
plete, there is a virtual cavity formed between it and the new diaphragm. 
Into this the nerve and blood-vessel are destined to pass, and within it 
also new muscle will be laid down. No cells come into the cavity except 
those of the blood, and all the tissues for the new limb are derived from the 
epidermis lining the space on the distal side. The old diaphragm, which 
has performed its work and is shrivelled and brown, now peels off, leaving 
bare the newly formed layer of cells across the stump. These are seen to 
have preserved at least this part of their original functional activity that 
they secrete a thin layer of chitin on their outer edges. Soon the layer 
thus laid over the cut end of the limb-stump is several cells thick, and 
