THE ANATOMY OF SCALIBREGMA INFLATUM. 283 



mens there are numerous small masses of excretory granules 

 distributed throughout the cells of the loop. These granules 

 appear dark brown or black when seen in masses^ but yellow 

 or light brown when examined singly. In some specimens 

 the deposits are in the form of yellowish needle-shaped 

 crystals. The nuclei of these cells are very small, and 

 situated very close to the lumen. The terminal tube closely 

 resembles the adjacent part of the loop, except that there are 

 fewer concretions in the former. On approaching the 

 nephridiopore the wall of the tube becomes thinner (fig. 20), 

 and in some specimens the cells of this part are not ciliated. 

 There is no muscular tissue in the walls of any part of the 

 nephridium. 



In some specimens Coccidian parasites, which in section 

 strongly resemble ova, are embedded in the cells of the loop. 



The nephridium is covered by a very thin layer of peri- 

 toneal epithelium, and the blood-vessels seen on the funnel 

 only lie between the peritoneum and the bases of the excre- 

 tory cells. 



Blood Supply. — The nephridia are supplied with blood 

 by branches of the afferent branchial vessels which are given 

 off from the dorsal vessel (as in the case of the first three 

 nephridia) or by the segmentally arranged branches of the 

 ventral vessel (fig. 14). The latter vessels usually bifurcate 

 near the setal sacs, one branch passing to the uephrostome 

 and the other to the body- wall; the latter vessel usually bears 

 blind outgrowths which partially obscure the nephrostorae. 



The nephridia receive only a small amount of blood, the 

 whole of which apparently goes to the funnel (and to the 

 rudimentary septum on which the gonads are formed). I 

 have not found vessels on any other part of the nephridium. 



The first three nephridia return blood to the second, third, 

 and fourth efferent branchial vessels. The nephridia of the 

 fifteenth and following segments return blood to the sub- 

 intestinal vessels. 



It is interesting to compare Danielssen's observations with 

 the foregoing. He evidently saw only the loops of the 



