344 MOORE. [Vol. XIII. 



opaque that its internal structure is made out with difficulty; 

 but the funnel may be seen to be suspended from it, and the 

 efferent duct to leave it. Sections of two species (PI. XXI, 

 Figs. 14, 15) show that the efferent duct passes along its inner 

 face, more or less imbedded in its substance, and rather nearer 

 to its dorsal margin; and further that numbers of simple tubules 

 are cut along its course. This, then, is the main plexus lobe, 

 and its interior is seen in sections (Figs. 14, 15, 17) to be 

 excavated by systems of irregular anastomosing canals. B. 

 parasita, as shown by the study of a series of sections, is 

 exactly like B. pulcherrima in this respect. In all of these 

 species the main plexus lobe is relatively small, and the acces- 

 sory lobe is larger and more conspicuous; this is especially 

 true of Branchiobdella instabilia. In Bdellodrilus philadelphi- 

 cus and Branchiobdella pulcherrima the former is relatively 

 larger and constitutes the greater part of the opaque mass. In 

 the latter species it is relatively thicker and narrower, in the 

 former a high flattened plate (PI. XXI, Figs. 14, 15). 



Although the separate nodules of B. illuminatus are not dis- 

 tinguishable in any of these species, the surface of the mass is 

 marked off into areas by grooves of greater or less depth, which 

 are filled by nests of connective-tissue cells, and give the body 

 a lobulated appearance, which is frequently seen in sections to 

 correspond with the internal arrangement of passages. Indeed, 

 the appearance of the entire structure is such as would result 

 if the walls of a tubule folded upon itself, as is that in the 

 plexus region of B. illuminatus, had fused along contiguous 

 faces, obliterating the external indications of the winding, 

 which is then further concealed by the connective tissue and 

 peritoneal coverings. As will be seen when the structure of 

 the tubule loops is discussed, we there find an actual fusion of 

 contact points along the tubules. Mutual pressure would dis- 

 tort the original nodules and compact and solidify the whole 

 organ. 



Whether the course of the lumen within this mass is the 

 same as in B. illuminatus could not be determined, but the fact 

 of alternating plexuses and ciliated canals is easily demon- 

 strated; and it is almost certain that there are no anastomoses 



