162 University of California Publications in Zoology [Vol. 11 



covered the larger part of the surface of the cover glass in con- 

 tact with the hanging drop of plasma. The boundaries of the 

 cells were mostly hexagonal and the appearance of the membrane 

 was very much like of the shed cuticle of the adult amphibian. 



Membranes like the one .iust described are called secondary 

 because by following the method of their formation it was found 

 that they were the result of the fusion of originally separate 

 cells. Many other similar membranes were observed to arise 

 from the implanted issue by the outgrowth of a continuous sheet 

 of ectoderm. The thickness of these outgrowths varied from one 

 to three or four cells deep. Generally they were thinner towards 

 the periphery, and the outermost cells usually presented a 

 thinned out and finely amoeboid margin. 



In many cases the ectodermic epithelium was drawn out into 

 very long strands. These usually became manifest in two or 

 three hours after the preparation was made, but they reached 

 their maximum extension as a rule in three or four days. Fre- 

 quently the length of the strands was several times the diameter 

 of the piece from which they originated, and they were usually 

 several cells in thickness, but occasionally were reduced to a 

 single row of overlapping cells. The cells were generally fusi- 

 form with the long axis parallel to the strand. As a rule these 

 strands were in contact with the cover slip, but they frequently 

 crept out upon the surface of a coagulated portion of the sur- 

 rounding medium. In several preparations fibers of cotton wool 

 were introduced, and where the epithelial cells came in contact 

 with the fibers they crept out upon them to a considerable distance. 

 It is common to find the fibers completely surrounded by an 

 investment of epithelium. The extension of epithelium always 

 occurred at some break in the surface. In figure 1 is shown a 

 piece of a cross section of the tail of a Hyla tadpole taken near 

 the tip. The epithelium had covered the posterior cut surface, 

 and at the meeting point of the approaching edges of the extend- 

 ing sheets of cells a long strand had grown out posteriorly, 

 reaching on the third day the extent illustrated in the figure. 



In a section of the tail of tadpole of Rana (pi. 7, fig. 2) there 

 is shown a similar posterior extension of ectoderm, but in addi- 

 tion there are strands proceeding from the anterior edge of the 



