396 E. S. GOODRICH. 



other regions possess, as a rule, one large nucleolus, and some- 

 times some small ones in addition. 



The fourth region of the nephridial canal leads directly to 

 the exterior by means of the nephridiopore (figs. 1 and 2 ; 

 fig. 10, neph.p.), which opens on the ventral surface of each 

 segment, about halfway between the ventral cirrhus and the 

 longitudinal muscles. In fig. 10 it is seen that the Avail of the 

 tube pierces the epidermis (fig. 10, ejo.), and reaches the cuticle 

 itself: near the pore are a pair of nuclei, one on either side of 

 the canal. 



The sections through the wall of the nephridial canal show 

 that it is lined by a more or less definite layer (figs. 11 — 14, 

 b. I.), which is formed of an apparently denser material 

 than that which lies outside. This boundary layer is very well 

 developed in the last region (fig. 14, b. /.). Running throughout 

 the substance of the nephridial mass is a delicate network of 

 some denser cuticular substance, which stains darkly with 

 hematoxylin (figs. 11, 12, 12a, b, 13, 14, 16, net.). The 

 boundary layer is pierced by the network, which thus reaches 

 the lumen of the tube, and forms a close network round it. 

 The cut ends of the threads of this network can be seen in 

 the longitudinal section of the lumen drawn in fig. 14. 

 Dr. Eisig describes in the Capitellids a somewhat similar 

 though coarser mesh-work, as continuous with a boundary 

 layer which he believes to be cuticular. In Nereis there 

 appears to be a supporting network, and a distinct boundary 

 layer, which is probably formed, not of cuticle, but of dense 

 protoplasm, filled with minute granules. In some sections of 

 a specimen preserved in Hermann's fluid (fig. 12 a, ves.) little 

 vesicles or vacuoles can be seen piercing this layer and opening 

 into the lumen, presumably between the meshes of the net- 

 work ; these vesicles probably contain some excretory products. 

 Fig. 12 b represents a small portion of the supporting net- 

 work, situated between the coils of the canal, in which are 

 seen some connective-tissue cells. These cells do not belong 

 to the wall of the canal, and their nuclei are smaller than those 

 of the lining cells. 



