UNIVERSITY OF CALIFORNIA PUBLICATIONS 



IN 



ZOOLOGY 



Vol. II, No. 8, pp. 155-172, pis. 7-8 September 24, 1913 



BEHAVIOR OF ECTODERMIC EPITHELIUM 



OF TADPOLES WHEN CULTIVATED 



IN PLASMA 



BY 



S. J. HOLMES 



The movement of epithelial cells in embryonic development, in 

 regeneration and in variou.s pathological processes has long been 

 recognized ; and an extensive literature has grown up in relation 

 to various phases of the .subject. But while the fact of such 

 movement has been generally regarded as established, there has 

 been considerable diversity of opinion as to the precise method 

 by which epithelial cells change their position and as to the causes 

 of their migrations. The formation of continuous epithelial 

 membranes is to a large degree a matter of the behavior of the 

 component cells. These cells have a marked tendency to arrange 

 tliemselves in layers, and to fit closely together so as to leave no 

 open spaces between them. The role of the latter tendency in 

 relation to various osmotic processes in the organism is obvious. 

 And we find that it is manifested as a rule by the cells of early 

 embryonic development. 



The bla.stula and gastrula in typical cases are composed of 

 cells forming a perfectly continuous layer enclasing a cavity 

 which contains fluid of a different osmotic pressure from that 

 of the surrounding medium, a condition that could not be main- 

 tained in the absence of a continuous membrane. Even in early 

 cleavage this tendency of the cells to fit together (the Cytarme of 

 Roux) is very manifest. Later the same trait manifests itself 

 in the formation of the germ layers, and the maintenance of the 



