174 Mary Isahelle Steele 



slight indications that it is preparing to close over. But the 

 quantity of material lying inside and out makes it impossible to 

 determine what tissues are taking part in closing the wound. 



During the next twelve or fifteen hours the changes are still not 

 clearly defined. The interior still presents a rather badly confused 

 mass of injured tissue. Near the edges of the wound, however, 

 there are evidences that the hypodermis has begun to push outward 

 to cover the cut surface. For the most part the wound shows a 

 smooth even surface which indicates that the passage outward of 

 the injured tissues has ceased and that a sort of equilibrium had 

 been established. The mass of tissue closing the cut seems to be 

 made up of a few hypodermal cells and cytoplasmic strands, a 

 considerable accumulation of blood cells and the nuclei of the 

 breaking down tissues of the eye. Around the edges of the cut 

 occasional strands of hypodermis with a very few nuclei can be 

 distinguished. 



Sections of an eye fixed about forty hours after the operation 

 show the beginning of crust formation. Almost the whole surface 

 has been covered. Judging by the reaction to stains, the part 

 which may be considered the matrix of the crust is formed by an 

 attenuated, chitinous secretion of the hypodermis. In this matrix 

 are embedded numerous nuclei of the injured tissues together with 

 a great many blood cells and a few hypodermal cells. In some 

 parts the crust is sharply marked off from the underlying tissues 

 by a space filled with coagulated plasma. Over one part of the 

 wound the crust is not yet fully formed. At this point hypodermal 

 strands containing elongated flattened nuclei are seen stretched 

 across the space still uncovered. The strands appear in two or 

 three layers with very few nuclei in each layer. No definite 

 centers of cell proliferation can be recognized at this time. 



After the crust has covered the cut surface it continues to increase 

 in thickness for two or three days, then hardens, turns a bright 

 reddish brown color and remains over the stump until a moult has 

 occurred. The crust takes no further active part in the heahng 

 and regenerative processes. Fig. 46 represents in a semidia- 

 grammatic manner the crust formed over the wound in a crayfish 

 eye about sixty hours after the operation. The crust is continu- 



