46 CALIFORNIA ACADEMY OF SCIENCKS. 



The HtriK'tiire of the uephridium i« considerably complicated. The uephiidio- 

 stoiue, found in front of the ventral setse, is uuusnally minute, and leads to a com- 

 partively short, duct, which connects with the body of the nepridium proper, at the 

 point where the single-tubed outlet leaves the folds. This tube is not convoluted (fig. 

 59(7)), but almost straight, very hard and solid, widening toward the base. When 

 it reaches the folds it does not at once enter a tube, but forms a long, cylindrical, 

 spongy mass (fig. 63), which extends the whole side or one-tliird of the lengtli of the 

 nephridium, before it assumes the proper shape of a clear canal (fig. 59, to 0, 

 and fig 64). In the beginning at 0, this mass shows no regular lumen, but a num- 

 ber of irregular pores and tubes, which miglit best be compared to the inner canals 

 of a common washing sponge (fig. 64, 0, 0, @). In the center of this mass are 

 imbedded the two parallel folds of the main nephridial canal (fig. 64, a and h). At 

 first the spongy tube is located jii'int'ip^dly 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. 64, to0). The small connecting tubules at 0, which were at first so ir- 

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

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

 (0, fig. 64) of the two central canals [a and b). 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, and the trans- 

 verse ducts drop into the main canal 0, while the former Icnver canal assumes 

 the character of a rather thick, epithelial lining. The general effect of this arrange- 

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

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

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

 rower. The length of this narrower |)art varies, but generally already at 0, or 

 shortly before entering on the bent plexus at 0, the fold has regained its oi'iginal 

 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 thi'ough 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 point it separates itself from the fold, and, running 

 along the inner body-wall, forms the outlet duct opening at the exterior pore at 0. 

 The connecting bridge between the two main folds, or rather between one fold and 

 the free lobe of the other, between and 0, is very narrow at 0, suddenly 

 increasing at 0, gradually tapering 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 difficult. The narrow 

 duct from the funnel to is ciliated as well as the funnel itself. Again, the ciliation 



