POSTURE OF MEMBRANOUS LABYRINTH 173 



region to the tip of the tail. Perhaps of a similar character is the 

 shifting of groups of ganglion cells within the central nervous 

 system as described by Kappers ('08) and the author (Streeter 

 '08). These, however, are movements of small clusters of cells. 



An example of intrinsic motility of a larger epithelial mass, 

 which will be more analogous to the ear vesicle that we are dealing 

 with, is afforded in the healing of skin wounds of young larvae. 

 The epithelial coat, in such cases, spreads like an elastic sheet 

 from the surrounding area over the wound. This mass-like move- 

 ment of the epithelial coat is very characteristic. On watching 

 the healing of a denuded area one can see the pigmented epithe- 

 lial layer gradually spread in from all sides of the wound, covering 

 in, as it does so, the exposed mesodermal elements, until even- 

 tually its edges tightly pucker together at the center. This is 

 accomplished not by the formation of new epithelial cells but by 

 the stretching out of the cells already there, as can be plainly 

 seen by the alteration of the pigment pattern. The marked 

 tension on the adjacent epithelium resulting from this movement 

 in the region of the wound is strikingly shown by the way in 

 which the pigment line existing along the dorsal crest of the larva 

 becomes deviated toward the operated side. In such cases the 

 epithelium belonging, we will say, to the left side of the body, is 

 drawn well over to the right side, thus indirectly aiding in the 

 covering of the seat of operation. For an excellent description of 

 the behavior of the epidermis in the healing of wounds in larval 

 Nectuinis, the reader is referred to the paper of Eycleshymer 

 ('07). If the epithelial ear vesicle can move and adjust itself to 

 varying conditions in the same way that the skin epithelium moves 

 and adjusts itself we could then understand the rotation of the 

 vesicles recorded in our experiments. 



A second possibility is that the nerve and ganglion mass may 

 serve to draw the vesicle into its proper position. At the time 

 of the operation some of the ganglion element is usually trans- 

 planted with the vesicle, and as the latter develops we find the 

 ganglion closely attached to the thickened part of its floor which 

 is to form the macula. At the same time fibers have grown out 

 from the central end of the ganglion to attach themselves to the 



