lyS Mary Isahelle Steele 



stages. But even the examination of a series of sections from the 

 same eye will show that the indications are strongly in favor of the 

 view that these hypodermal cells remain active and constitute the 

 hypodermis during the subsequent regenerative processes. Fig. 

 53 is taken from the same eye as d in the series shown in Fig. 52. 

 In the later figure it is evident that regeneration is in progress. 

 The hypodermal cells, however, show a tendency toward a paired 

 arrangement indicating that they are the original hypodermal 

 cells. 



After a part of the corneal covering has been removed it is 

 evident that an entirely new hypodermis must be regenerated over 

 the wounded surface. In crayfish it was seen that active cell 

 proliferation began near the edges of injured hypodermis and that 

 new. cells pushed outward from these centers. The early stages 

 have been examined in a number of eyes of Palaemonetes. The 

 centers of cell proliferation in this form are not so apparent. The 

 nuclei which in the early stages appear beneath the cuticle that 

 covers the wound are very few and lie far apart. Their number 

 increases not chiefly by the repeated multiplication of nuclei at the 

 edges of the wound but by the repeated division of the nuclei that 

 are pushed out onto the wounded surface. During these early 

 stages while the nuclei are actively dividing the cytoplasm is very 

 loose and reticular and the cell boundaries are indistinguishable. 



In many cases the new cuticle which becomes apparent after the 

 first moult is somewhat definitely separated into a dense outer 

 portion and a semifibrous inner division. The inner division 

 often appears as an interlacing network of fine fibers, many of 

 which can be traced into the hypodermis beneath (Fig. 53). The 

 loose incompact character of the hypodermis over the wounded 

 surface probably indicates a high degree of activity of the hypo- 

 dermis in this region. 



It is apparent from the foregoing description of the formation 

 of the hypodermis covering the wound that the regenerated hypo- 

 dermal cells may arise in two ways. They may arise by a trans- 

 formation of the old corneal hypodermal cells in situ in which 

 they assume a less specialized role or they may arise by the migra- 

 tion of a limited number of hypodermal cells from the edges of the 



