ON THE ANATOMY OP HISTRIOBDELLA. HOMARI. 305 



the nepliridia, and its action more feeble than that of the 

 others, as the motion of its Hagella is the first to stop when 

 the animal is compressed under a cover-slip. It, however, 

 •assumes a much darker colour on impi-egnation with methyl- 

 blue than do the other nephridia, and for this reason seems to 

 play a considerable part in the excretion of waste products. 

 Its position in the male has been correctly indicated by 

 Foetting-er, who remarks that no organ is to be found in 

 this position in the female. 



Unlike Strati odrilus, the organ does not begin in a loop 

 •or run back so far in the tail region, but opens on the exterior 

 just over the line of separation between the generative and 

 the caudal segments (fig. 12). 



4. Body-Cavity and Nephridia. 



As in Dinophilus, there is an extensive blastocoelic cavity 

 surrounding the gut, which sends prolongations into the head 

 region, and also into the anterior and posterior feet. It has 

 been described by Foettinger as lined by a more or less 

 definite coelomic epithelium. I cannot find that this is strictly 

 the case. The gut surface of the cavity is covered by a 

 delicate cuticle, in which at rare intervals are seen small 

 flat nuclei. It is difficult to say if this membrane is a definite 

 structure or a mere secretion from the blastocoelic ends of 

 the cells of the gut-wall. The soraatopleuric side of the cavity 

 is not lined by any such membrane. The longitudinal muscles, 

 as in Stratiodrilus, are surrounded by a similar delicate 

 cuticle, but no nuclei are to be seen in it as in the gut 

 membrane. I believe in neither of these cases can this 

 membrane be considered a true peritoneal or ccfilomic epithe- 

 lium. No mesenteries are present, nor can I observe the 

 fusion of the gut to the dorsal ectoderm as mentioned by 

 Foettinger. The gut is more or less closely applied to the. 

 dorsal Avail, but I cannot find that any true fusion takes 

 place. 



In the head the blastocoelic space sends prolongations into 



