Iti CAI.ll DUMA AIAI>KMV nl x IKM'Ks. 



Tlic sinicliiic lit tlic n(|pliri<liiiiii is foii.sidenihly complicalcil. 'I'hc iic|iliri<li()- 

 stome, t'oiiiKl ill front of the ventral .sct.e, is unusually minute, and leads to a eom- 

 |>ailivelv short duct, which connects with the hody of the nepridinin proper, at the 

 point where the sin<;le-tul)ed outlet leiives the folds. Tiiis tuhe is not eorivoluteil ( lij^. 

 ")I)(T)), hut almost straight, very liard and solid, widening toward the l)asc. When 

 it reaches the folds it does not at once enter a tuhe, hut forms a long, cylindrical, 

 spoiigv mass (fig. (>'S), which extends the whole side or one-third of the length of the 

 nephridium. In'fore it assumes the proper shape of a clear canal (lig. ."iiJ, to 0, 

 and fig CA). In the beginning at 0, this mass shows no regidar lumen, hut a inim- 

 her of irregidar pores and tuhes, which might best be compared to the inner canals 

 of a common washing sponge (fig. 04, 0, 0, 0). In the center of this mass are 

 imbedded the two j)arallel folds of the main nephridial canal (fig. HA, n and li). At 

 first the spongy tube is located princi[)ally above the two canals, but soon the mass is 

 shifted and the canals become imbedded in the center of the mass, or very nearly so 

 (fig. G4, 0to0). The small connecting tubules at 0, which were at first so ir- 

 regular, soon assume a greater degree of regularity at 0, while at the same time two 

 longitudinal lumens are formed — one on the upper and one on the under side 

 (0, fig. 04) of the two central canals {n and A). At first these canals and 

 are indistinct and irregular, but soon they assume the character of regular longitudinal 

 canals (from to 0, and 0). From to these canals and are 

 connected by the transverse tubules, which completely surround the two central 

 canals and 0. At the lower canal becomes narrower, anil the trans- 

 vei>>e ducts drop into the main canal 0, while the former lower canal ixssumes 

 tlu! character (»f a i-alher thick, epithelial lining. The general effect of this arrange- 

 ment is, that, seen with a lower power, the spur between and appears to con- 

 sist of four distinct parallel canals, while from to the fold contains only three 

 paralhd canals. At these canals become very crowded, the whole fold being nar- 

 rower. The length of this narrower pai't varies, but generally already at 0, or 

 shortly before entering on the bent plexus at 0, the fold has regained its original 

 width. At the canals turn; that is, connects with and the central canal 

 folds upon itself, and for a short distance we have four almost parallel canals. At 

 the formerly central canal (from to 0, and 0) leaves the lobe and crosses 

 over to the other' fold, and at becomes the original canal 0, which runs its 

 course all through the two folds, at turning downward, becoming the lower canal, 

 which again at becomes canal 0, from there on pressing backward and again 

 forward from to 0, at which jwint it separates itself from the fold, and, running 

 along the inner body-wall, forms the outlet duct opening al ilic I'Xterior pore at 0. 

 The connecting bridge between the two main folds, or ratlur- ln'tween one fold and 

 the fre(! lobe of the other, between and 0, is very narrow at 0, suddenly 

 increasing at 0, gradually ta[)eriug toward 0. As regards the ciliation of the 

 canal, it may be stated that it does not extend all through the tube. It appears that the 

 canal is ciliated at places where the passage of the excretions is diflicidt. The narrow 

 duct fr.iin the funnel to is ciliated as well as the funnel itself, .\gain, the ciliation 



