EPIDERMIS WHEN CULTIVATED OUTSIDE BODY 291 



sequence of the activity of the cells themselves. Osowski, how- 

 ever, does not look upon the movements of the cells as amoeboid. 

 The general conclusion to which he comes in regard to the move- 

 ments of epithehum in the forms which he studied is: 



Die Beweguna-, die in den Explantaten zu Wunduberkleidung fiihrte, 

 gehort also zu der Rubrik der Selbstbewegung, und zwar zu den aktiven 

 Massenliewegungen des Epithets, weil sie sich an einer zusammen- 

 hiingenden Masse von Epithelzellen gemeinsam a1)spielt. 



Vergegenwiirtigen wir uns das im experimentellen Teil iil^er den 

 Vorgang der Wundbedeckung Gesagte und beachten wir die beigegeben 

 Figuren, so wird man in der Bewegung alle Charakteristika der von 

 Oppel so genannten "Epithelbewegung" wiederfinden : Sie vollzieht 

 sich ohne Pseudopodienbildungen, die Zellen bewegen sich hinter — 

 und nebeneinander sowie parallel zu der zu iiberkleidenden Olierfliiche. 



Osowski's failure to find pseudopodia is, I think, due to his 

 study of preparations by means of serial sections, and to the 

 fact that his studies of living material were made by observing 

 the epithelium in contact with other parts of the implanted tissue. 

 The pseudopods of epithelial cells of amphibian larvae are so 

 short and so fine that it would scarcely be possible to detect 

 them when they were extending upon other parts. Only when 

 these epithelial cells become freed so that one can observe their 

 free margin with high powers of the microscope is it possible 

 to ascertain the real method of their movement. Apparently 

 neither Osowski nor Oppel observed epithelium extending away 

 from the implanted tissue. This was due doubtless to the em- 

 ployment of Ringer's solution, which does not evoke a thig- 

 motatic reaction from the cells. 



I am compelled therefore to dissent from the view that the 

 movement of epithelium in amphibian larvae takes place ac- 

 cording to the conception of "Massenbewegung" as described by 

 Oppe^ and adopted by his co-worker Osowski. Study of epi- 

 thelial cells under the favorable conditions of isolation where 

 they are spread out on the under surface of a cover slip clearly 

 shows the essentially amoeboid character of their movements. 



® Oppel, A. Causal-morphologische Zellenstudien. V Die aktive Epithel- 

 bewegung, ein Faktor beiin Gestaltungs- und Erhaltungsgeschehen. Arch. f. 

 Entw-mech. Bd. 35, 371, 1912. 



