ON HvEMONAIS LAURENTII. 779 



animal to the number of one to three on each side. These are 110 m in length, and 

 stout, 4 M in diameter. They were not seen to project from the surface, and were 

 revealed only in sections, where their distal ends were found to be at the level of the 

 superficial epithelium. The shaft is slightly curved, and the distal end is strongly 

 hooked and bifid. The two prongs of the fork are short, and equal in length, but 

 the proximal of the two is very much thicker, at least three times as thick as the 

 distal. The nodulus is markedly distal to the middle of the shaft, less than a quarter 

 (approximately f ) of the length from the distal end. 



The alimentary canal also undergoes changes in the sexual animal similar to, 

 though on the whole not (in these specimens) as marked as, those which occur in 

 Dero limosa (cf. post, p. 785). The description which follows relates for the most 

 part only to the most advanced stage of sexual maturity ; this has not quite been 

 reached in the specimen from which figs. 4, 5, 6 have been drawn. 



The mouth opening persists ; but the pharynx disappears as a distinctive structure, 

 and the anterior part of the alimentary canal forms a narrow tube lined by a low 

 epithelium or by cells with no regular epithelial arrangement. In what is perhaps 

 an earlier stage of degeneration there is seen, dorsal to the alimentary tube in the 

 region formerly occupied by the pharynx, a considerable mass, with nuclei but 

 without cell-limits, from which muscular strands radiate towards the parietes. This 

 mass, though now separated from the wall of the tube, apparently represents the 

 dorsal diverticulum in this region, previously described. 



The lumen is still present in segment iv, but disappears in v ; narrowing, the 

 oesophagus becomes in vi merely band-like, and smaller in transverse section than the 

 ventral nerve cord ; indeed, it may almost disappear altogether, and in certain 

 sections it could hardly be recognised if it were not for the investment of chloragogen 

 granules. As far back as segment ix it continues very narrow, approximately 10 v 

 in diameter (exclusive of the chloragogen investment) ; there is no lumen, and the 

 solid cord is hardly more than one cell thick ; small vacuolar spaces are seen here 

 and there, though the cells do not seem to be in the last stage of degeneration. 

 Behind this level it gradually widens, and the lumen reappears in segment xi. 



In the posterior part of the body the lumen is well marked, though filled with 

 non-staining granular matter. The epithelium is low, scarcely more than cubical, 

 but is not markedly degenerate. 



Parasite. — In an early sexual individual a relatively huge sporozoan parasite was 

 found to be occupying the ccelomic cavity about the middle of the animal's length. 

 It was somewhat twisted, but its length was estimated at not less than '8 mm., perhaps 

 as much as 1 mm. ; in breadth it was '09-12 mm. Other stages were seen in several 

 specimens here and there in the alimentary wall ; and in all specimens with a well- 

 developed sperm sac this latter contained- very numerous small spherical bodies 

 about 20 fj- in diameter, with ill-defined nuclei, presumably belonging to the same 

 life-cycle (fig. 5,^>.). 



