100 Transactions. — Zoology. 



entire specimens stained and cleared. From the point of view 

 of the comparative anatomist the results obtained are hardly 

 sufficient to compensate for the large expenditure of time and 

 trouble, as in most respects the anatomy seems to agree very 

 closely "with that previously known for other species of the 

 genus. The structure and arrangement of the nephridia, 

 however, appear to be very peculiar, though we have not 

 succeeded in working them out in detail, and the presence of 

 only two annuli in the typical somite appears to distinguish 

 our species not only from others of the same genus, but from 

 all other ffliynchobdellida r~ 



External Chabactebs. 



In contracted specimens the body is ovoid; emarginate and 

 somewhat broader behind ; strongly convex above and con- 

 cave beneath, so that there is a large hollow space below the 

 body which serves as a brood-pouch ; with no distinct head. 

 The length of a spirit-preserved specimen was 6 mm., and 

 the width 4 mm., with posterior sucker l - 5mm. in diameter. 

 Another specimen, when extended in life, measured as much 

 as 18 mm. in length. The animal in life is of a very pale 

 dull orange or flesh-colour, semitransparent, with no papillae 

 nor colour-markings except microscopic pigment-cells. In 

 spirit the colour is almost white, opaque. 



The posterior sucker (disc) is flat, and usually nearly 

 circular in outline ; in contracted specimens scarcely visible 

 from above. The much smaller anterior sucker appears to be 

 made up of from five to eight annuli! (it is impossible to 

 determine the exact number), and its anterior margin, form- 

 ing the extreme anterior end of the body, bears a slight 

 median notch. 



On the dorsal surface of the body about fifty-five annuli 

 may commonly be counted, but the annulation is not suffi- 

 ciently distinct and regular to make an exact count practi- 

 cable. In the middle region of the body it is evident, from 

 the arrangement of the nephridial apertures and various in- 

 ternal organs, that each somite is composed of two annuli. 



The eyes are four in number, placed two on each side of 

 the middle line, those of the same side very close together, 

 sometimes touching one another, so as to appear as one in 

 contracted specimens, but separated from those of the oppo- 

 site side by a fairly wide interval. Their position is about on 

 a level with the hinder margin of the anterior sucker. Those 

 of one side may be distinctly in advance of those of the other 

 side, and the position as regards the annuli of the head seems 



* See Postscript, however. 



t In counting the annuli we assume throughout this paper that the 

 head (anterior sucker) is made up of eight. 



