Gatty Marine Laboratory, St. Andrews. 27 



the outer ends of the ventral longitudinal muscle. The 

 nuclei along the sides of the tuhe stain deeply, thus outlining 

 the canal which curves downward and outward and opens 

 helow the bristle-tuft external to the outer edge of the 

 ventral muscle (PI. II. fig. 13, so.). Nothing was seen of 

 its internal connections except an occasional wider section. 

 Separate masses of the deeply stained cells were noticed here 

 and there, as if from folding or lobulation of the main tube, 

 which in some cases appeared to form loops, and the vascular 

 supply is abundant. Occasionally masses of minute cells 

 were present toward the middle, attached by mesenteries to 

 the other parts of the organs, and in section such were 

 sometimes circular. The ducts seem to be smaller and 

 longer posteriorly, and in some cases did not appear to be 

 functional, especially toward the tip of the tail. Further 

 investigations in this region are, however, necessary. When 

 the nephridial tubes are cut longitudinally the nuclei 

 ranged along each wall are conspicuous. 



In Amphiglena mediterranea the chordoid arch supporting 

 the branchiae is narrow and composed of but two large cells 

 from side to side of the middle of the bar, which is boldly 

 curved ventrallv at each end, whilst the central bar is 

 concave dorsally beneath the dorsal groove — the whole 

 having the form of certain bows, especially as a blunt conical 

 projection occurs at each end of the transverse bar where 

 the cells also are increased. The mouth in section in this 

 region forms a vertical slit, bifid dorsally — that is, leaving a 

 median pointed cone dorsally. The cephalic ganglia occupy 

 a similar position to that of the typical forms. The pharynx 

 soon forms a thick-walled tube rounded in section, and filled 

 with granules and spicules, the mesentery holding the dorsal 

 vessel above and the ventral inferiorly, the latter being close 

 to the two nerve-cords which lie on the inner surface of the 

 massive and continuous hypodermic glandular area of the 

 region and at some distance from each other, the compara- 

 tively massive ventral longitudinal muscles being as yet to 

 their outer border and wide apart, whilst the ventral blood- 

 vessel is placed between them. No neural canals are 

 present. Proceeding backward the ventral longitudinal 

 muscles, which are now extended and comparatively thin, 

 send their inner edges into the median groove formed in the 

 centre of the ventral hypodermic mass, the nerve-cords, 

 which were very indistinct in the preparations, apparently 

 lying at the sides of the fissure, in the middle of which is the 

 mesentery from the alimentary canal fixed to the distal end 

 of the fissure. About the level of the nerve-cords is the 



