BEHAVIOR OF CELLS IN FUNDULUS HETEROCLITUS. 223 



and in one of these the heart was still beating at the time of 

 fixation. In one culture peristalsis was observed in a portion 

 of the intestine which projected out into the medium. Con- 

 tractions of the trunk musculature, beating of the heart, and 

 movements of the fins were frequently observed in cultures 

 several days old. 



BEHAVIOR OF ECTODERM CELLS AT CUT EDGES. 



In normal embryos the ectoderm consists of a single layer of 

 large pavement cells, polygonal in surface view, which may be 

 clearly seen in the regions covering the fins and the trunk mus- 

 culature. The cells are transparent and almost colorless. The 

 internal structures are only vaguely visible. The cells covering the 

 trunk have delicate concentric markings, suggesting somewhat 

 the markings upon fish scales. 



When the embryos are cut the ectoderm cells along the edge 

 round up very markedly into spherical masses, especially in the 

 region of the heart and the yolk sac. Any small group of cells 

 or single cells that have in cutting become separated from the 

 explant remain for some time in this state. Eventually, large 

 vacuoles develop in them and they remain inactive in this con- 

 dition for several days before disintegration takes place. Similar 

 cells were frequently observed in old cultures along the edge of 

 the ectodermal membrane. 



The direction of the cut is a factor in the successful growth of 

 cultures from the trunk region of the body. The cells do not 

 grow out unless the cut is irregular or oblique. If it is transverse 

 the cells close in and form a covering over the injured end, 

 preventing outward migration. Osowski found that injured 

 surfaces of fish embryos were covered by an epithelial membrane 

 within twenty-four hours. 



Membranes never grow out from cut fin surfaces; the cells 

 near the cut surface become wrinkled and irregular in contour, 

 and remain in this condition sometimes for several days, before 

 they become rounded up and display the large vacuoles and 

 greenish protoplasm which are characteristic of degenerating 

 ectoderm cells. Sometimes the ectoderm of the fins degenerates 



