1 90 Mary Isahelle Steele 



ating eye in Crangon than in either Palaemonetes or hermit crabs. 

 The whole of the eye stalk in Crangon is thickly covered with 

 branching pigment cells. So that even after the eyes are brought 

 into oil very little can be seen in detail by examining them in toto. 

 Figs. 7 and 8 thirty-one and thirty-two days, respectively, are 

 fairly characteristic of the regenerating eye of Crangon. From 

 all that can be determined from the outside, regeneration seems 

 practically complete in each of these cases. Sections show, 

 however, that comparatively little regeneration has taken place. 

 A fuller discussion of the regenerating eye of Crangon will be taken 

 up elsewhere. 



2 Details of Development of the Regenerating Ommatidia 



The complete regeneration of the ommatidial portion of the eye 

 involves three stages. These can be separated from each other 

 rather sharply although they overlap more or less. The first stage 

 consists in getting rid of the broken-down tissues and the healing 

 of the wound; second, the active proliferation of new cells; and 

 third, the differentiation of the new ommatidia. The first and 

 second stages have been discussed in Section IV. 



a Regeneration of Retinulae 



All the observations support the conclusion that the regenerated 

 ommatidia are derived entirely from the hypodermis. Before the 

 hypodermis covering the end of the stump has been clearly difi^eren- 

 tiated, however, the proliferation of cells for the new structures 

 lying below has begun. So that at the same time hypodermal 

 cells are dividing in two planes, one at right angles to the periphery 

 to increase the number of hypodermal cells, and the other parallel 

 to the surface. The inner nuclei of the latter division migrate 

 inward and become the first retinular cells. As they migrate they 

 become elongated with their long axes radially arranged. 



Fig. 54 shows the early stages of the separation of retinular 

 nuclei, some separating from the nuclei at the periphery and others 

 migrating in. At a comparatively early date these retinular 

 nuclei have migrated a considerable distance below the surface 



