BEHAVIOR OF CELLS IN FUNDULUS HETEROCLITUS. 23! 



be gradually weakened and the adhesive power progressively 

 increased as the cells spread out in a thin layer upon the under 

 surface of the mesenchyme. Holmes ('13) found that ectoderm 

 cells of tadpoles in tissue cultures attach themselves readily to 

 various kinds of substrata, including the cover glass, and "extend 

 upon one another in mutual attraction which tends to keep them 

 in continuous masses." In fundulus, however, this stereotropic 

 activity of the ectoderm is called forth only when the cells are 

 associated with the mesenchyme, and it appears to be much 

 stronger than in the frog, causing the cells to be spread out in a 

 thin single-layered membrane. In over fifty cultures it was 

 never observed that an ectodermal membrane grew out unac- 

 companied by mesenchyme, whereas numerous cultures contained 

 growths consisting of mesenchyme alone. The latter cells 

 appear to be more highly stereotropic than the ectoderm, for 

 they will adhere to the smooth surface of the cover glass even to 

 the extent of having their processes snapped off when the ecto- 

 derm retracts. 



The difference in behavior of the two layers of cells is perhaps 

 correlated with the fact that under normal conditions of develop- 

 ment ectoderm cells grow only in contact with the mesenchyme, 

 whereas mesenchyme cells can grow in contact with widely 

 varying kinds of surfaces. 



The question arises whether there is any relation between 

 wound-healing and the formation of the ectodermal membrane 

 in tissue cultures. Loeb ('20) has discussed various processes 

 involved in cell movements in wound-healing, designating among 

 others amoeboid migration of ectoderm cells, this being "the 

 first response of the tissue to the wound stimulus." A factor 

 in this amoeboid wandering of the ectoderm cells is their stereo- 

 tropic reaction, as expressed by their contact with the coagulum, 

 which is "the foundation for the process of wound healing." 

 In fundulus cultures the wandering of the cells in contact not 

 with a coagulum but in this case with the mesenchyme layer is 

 the foundation for the process of formation of the ectodermal 

 membrane. The manner of cell movement, however, does not 

 appear to be amoeboid in character. 



