The anatomy of the leech Haemopis sangaisaga is described. Whereas all other descriptions of British leeches are based on Whitman's conception of the relation between annulation and segmentation the system here employed is that of Castle and Moore, in which the distribution of the peripheral nerves is used to define the limits of the segments.
The alimentary canal differs markedly from that of Hirudo, since the crop has only one pair of lateral diverticula. This may be correlated with the feeding habits, which are macrophagous and not sanguivorous.
The nephridia are described in particular detail. It is found that, as in Hirudo, the inner end of the nephridial tubules have lost their connection with the ciliated organ, and the latter has no excretory function, but manufactures coelomic corpuscles.