738 



one of 27 mm is, however, noticeable in the region behind the second 

 nephrostome. The smaller Axolotl showed no arrangement of the cells 

 of the thickening here; the larger one not only exhibits greater pro- 

 liferation, but in the middle of the epithelial cell-mass a distinct rod 

 of cells appears (Fig. 3). For a few sections at a time the rod be- 

 comes indistinct, but it only merges in the cell-mass, and reappears a 

 little further back. The cells of the rod are compactly put together, 

 and seem to have separated themselves from the neighbouring cells. 



Through many sections the thickening can be distinctly traced 

 outside of, and perfectly distinct from, the segmental duct. Towards 

 the posterior it diminishes greatly in extent, so as to resemble in 

 character the anterior part of the thread that was described as pas- 

 sing back from the second nephrostome in the 25 mm specimen. At 

 certain places it consists simply of three or four heightened epithelial 

 cells (Fig. 4). 



Passing now from early stages in the development to some of 

 the later ones I shall first refer to the growth of the duct towards 



Fig. 1. 



