Gaily Marine Laboratory ^ St. Andrews. 257 



above the duct of a mucous gland, impinging on the wall of 

 the blood-sinus on one side, and apparently attached to the 

 depression in the hypoderm and indicative of an opening in 

 the mid-lateral region. The epithelium in the food*-canal 

 differs quite from that in front, being almost fibro-granular 

 in aspect from the elongation of the cells, the nuclei of which 

 lie toward the outer border, and at first the surface presents 

 reticulations. The alimentary canal enlarges behind the 

 foregoing, but the character of the mucous lining remains 

 the same, and the ventral blood-vessel lies in the mesentery 

 over tlie nerve-cord, which is large^ with a median peak 

 dorsally and a specially thickened hypodermic layer at each 

 side. On the dorso-lateral regions of the body the hypoderm 

 appears to be thicker than on the mid-dorsal and mid-lateral 

 parts. No specialized dorsal blood-vessel appears in this 

 region, for it has fused with the sinus. 



In horizontal longitudinal section (PI. XI. fig. 23) the 

 alimentary apparatus has a similar appearance at the second 

 septum to that shown in Owenia, though the details are 

 slijihtly different and the scale is much less. The mucous 

 lining is thickened as it approaches the septum, and a 

 ctntro-lateral fold bulges forward into the stomachal or 

 gizzard-like division, whilst the central opening is narrowed 

 and enters the succeeding part of the alimentary canal as a 

 prominent papilla. The narrow termination of this region 

 stains more deeply than the rest; indeed^ it is coloured like 

 the muscular se[)tum, so that it is probable that it has 

 specially developed muscular fibres at this part so as to 

 enable it to perform sphincter-like functions, the food being 

 retained in this chamber for some time and then permitted 

 to pass backward by relaxation of the muscular guard. 



In vertical sections of the middle region the gut is at first 

 flask -shaped, the wide part, with the contents, being dorsal, 

 the narrow part ventral ; and the mucous lining has again 

 altered its character, the cells being larger, their nuclei 

 larger, and the inner edge smooth. The coelomic si)ace in 

 the female is distended on both sides with large ova having 

 a clear nucleus, an opaque nucleolus, and granular contents, 

 and they spring from the epithelium of the mesentery below 

 the ventral blood-vessel, the smaller ova being inferior, the 

 larger su|)erior. A noteworthy change is the disappearance 

 of the blood-t^inus around the gut and the presence of a 

 dorsal vessel in the upper mesentery, the ventral trunk 

 remaining as before. The thick layer of hypoderm ventrally 

 has a furrow over the median nerve-cord, and this coat i» 

 comparatively thin laterally and dorsally. The dorsal and 



