306 W. BLAXLxiND BENHAM. 



At the apex of the loop the middle tube opens into a bladder- 

 like enlargement (C) of the tube, called by Gegenbaur the 

 "ampulla;" this is the commencement of the " wide tube." 

 The ampulla is bent sharply upon itself, and gradually nar- 

 rows in diameter till it reaches about twice that of the middle 

 tube, which it retains throughout its course. There are no 

 cilia in this part of the tube, notwithstanding Goehlich's 

 statement that it is ciliated. 



The wall of the ampulla is very different from that of the 

 other regions. The cells are relatively very large, but are still 

 "drain-pipe^' in nature; their general arrangement and their 

 shapes are shown in a figure taken from a living though mori- 

 bund specimen (figs. 12, 30). The substance of the cell is 

 divisible into two well-marked parts, a central and a peri- 

 pheral portion (see figs. 13, 15), easily recognisable in a living 

 nephridium. So marked is the distinction between the two 

 parts, that in section it appears as if the perforated cells were 

 surrounded by others, as Beddard (4) suggested might be the 

 case in his description of All ur us; but such is not the case. 

 A series of sections and examinations of living nephridia show 

 that this appearance is really due to the modification of the 

 protoplasm bordering the lumen. 



The central portion of the protoplasm, which forms a thin 

 lining to the lumen, is made up of numerous small granules 

 arranged radially, giving the impression of a radial striation 

 (figs. 13, 15). In preparations stained with borax carmine 

 these granules take the dye much more strongly than the other 

 parts of the nephridium, and give this ampulla a very charac- 

 teristic appearance. The peripheral portion, which surrounds 

 the central portion, forms a much greater bulk of the cell, and 

 possesses much smaller granules, amongst which the nucleus 

 is situated. The granules here also are arranged in rows, 

 though less distinctly than in the central portion. A peculiar 

 appearance, as of nuclei, is presented sometimes by this peri- 

 pheral portion of the protoplasm : deeply stained, usually 

 irregular, though sometimes regular, masses of different sizes 

 are present (fig. 15). As a rule each mass, or sometimes a 



