Wound Reparation—A ctiman Tentacles 193 
tension in the epidermal sheet, this tension being due to a tendency 
of each individual cell to flatten itself so as to cover a maximum 
surface. 
In the earthworm (Rand ’o4) the closing of a wound involves 
three factors. (These statements refer to the healing of an ante- 
rior cut end. Conditions at a posterior cut end are in certain 
respects different from those at an anterior cut end, as [ shall 
show in a paper now in preparation.) First, immediately after 
transection of the body, contraction of the muscle layers in the 
vicinity of the wound ensues, whereby the wound surface is con- 
siderably diminished in area. In the second place, a cicatricial 
plug is formed, closing the exposed coelomic cavity. The material 
of this plug appears to be chiefly leucocytes, which are probably 
transported to the region of the wound by means of the extensive 
forward flow of body fluid which occurs immediately after the 
cutting. ‘Then, thirdly, the epidermis advances from the region 
of its cut edges across the surface of the cicatrix so as either to 
cover over the cut end completely, or else to establish connection 
with the epithelial layer of the digestive tube. During this ad- 
vance of the epidermal layer the cells collectively always present 
to the exterior a smooth and continuous surface, yet the move- 
ment of the layer as a whole is distinctly conditioned by the inde- 
pendent migratory movement of the individual epidermal cell. 
No cell-division takes place during this process. 
In the stem of Tubularia and in Hydra we have a relatively 
simple kind of organization and transection produces a wound of 
small area as regards both cut tissue and exposed cavity. In the 
earthworm the organization. is of much greater complexity and 
transection results in a relatively large wound involving many kinds 
of cut tissues and the exposure of large cavities. Under the former 
conditions the method of wound closing is a comparatively simple. 
one; under the latter conditions it is more complex. What, then, 
we may inquire, would be the manner of reaction to transection 
in the case of a tubular structure possessing the simpler organiza- 
tion of Hydra, but whose dimensions are more nearly like those of 
the earthworm! ‘The possibility of obtaining an answer to this 
question was suggested to me by the luxuriant size of certain 
