232 PAULINE H. DEDERER. 



Oppel ('13) has described the bending of the skin edges along 

 the cut surface of explanted pieces of the tadpole's tail as due 

 to real movement; not simply a mechanical process but a change 

 in form by which the ectoderm grows around the cut. In an 

 earlier paper ('i2a) he compares the ectoderm cells to partly 

 rilled sacs of inelastic material which can change their outline 

 without varying the extent of their surface. This kind of move- 

 ment is strikingly similar to the early changes which take place 

 when the rounded cells begin to flatten. Oppel ('126) distin- 

 guishes between epithelial movement, which is a mass movement, 

 and amoeboid motion which tends to isolate cells, as in connective 

 tissue. He concludes that while the movement of the epithelium 

 depends on the activities of the cells themselves, it is not an 

 amoeboid motion. The observations on fundulus confirm this 

 interpretation. Here epithelial movement appears to be a mass 

 movement throughout all stages in the formation of the ecto- 

 dermal membrane. Single functional epithelial cells are never 

 found. 



In conclusion it may be stated that the activities of the cells 

 in the formation of the ectodermal membrane in fundulus are 

 similar to activities displayed also by ectoderm cells in the process 

 of wound-healing. As in the latter, the cells exhibit mass 

 movements the end result of which is to cover the connective 

 tissue; so in tissue cultures of fundulus the migration of the 

 ectoderm cells proceeds by mass movement which results in a 

 partial covering of the mesenchyme layer. The contact reaction 

 toward underlying connective tissue, exhibited by ectoderm cells 

 in wound-healing, is paralleled by the stereotropic activity of 

 the ectoderm cells evoked by contact with the mesenchyme. 

 It may be said that the cells are attempting to follow out their 

 normal activities, although subjected to abnormal conditions. 



SUMMARY. 



1. Tissues of Fundulus heteroditus grew in fluid media under 

 conditions varying widely in respect to temperature, concentra- 

 tion of salts, and character of nutritive substances. 



2. Mesenchyme cells migrated out into the medium upon the 

 under surface of the cover-glass and formed almost continuous 



