242 Prof. M'liitosh's Notes from the 



gullet proper (which may have complex functions), sur- 

 rounded by a tough (muscular) investment, from which 

 various strands radiate to the body-wall amongst the blood- 

 vessels of the region. The body-wall at this i)art has a 

 thinner coat of hypoderm both mid-dorsally and mid- 

 ventrally, its thick layer being lateral. The longitudinal 

 muscles form a somewhat thin layer of fasciculi all round, 

 and the lip-organ shows a thick mass of modified vertical 

 cells with nuclei, each mass probably lubbiug against the 

 other. The massive lip-organ then forms a thick-walled 

 tube in section, WMth a central cavity (PI. VII, fig. 5) and 

 an external muscular investment, whilst the oesopiiagus has 

 a thick mucous layer, continuoTis w^ith the hypoderm, to 

 subserve its special functions, the radiating strands and 

 numerous blood-vessels still continuing. 'I'hese radiating 

 fibres show that the movements of this thick-walled region 

 (PI. VIII. fig. 18) must be more or less restricted, yet the 

 longitudinal bands, especially on its dorsal wall, would point 

 to protrusion and retraction. Externally the hypoderm — 

 thickest laterally at and above the nerve-cords, vrhich are 

 descending — has increased in depth dorsally, but is thin 

 ventrally. Behind the foregoing the lip-organ loses its 

 central cavity (a fold) and diminishes in size, but its complex 

 muscular coat is proportionally thicker,and in thesurrounding 

 area the blood-vessels are larger. Finally, the muscles of 

 the lip-organ alone are visible, and then disappear, showing 

 that it is, in short, attached by a muscular stalk, first hollow 

 and tlien solid, though the sections would indicate that the 

 muscular fibres (retractor) are fixed to the body-wall close 

 behind and for some distance backward. Moreover, a fan- 

 shaped ariangement (PI. XII. fig. 17) occurs anteriorly 

 "where the fibres spread into the lip-organ. Besides, various 

 oblique and transverse fibres act on the folds and give 

 complexity to the movements (PI. XI. fig. 16). A double 

 layer of muscular fibres, further, lies beneath the basement- 

 tissue bounding the gland-cells — the one the reverse of the 

 otlier, — so that in sagittal section the cut ends of one series 

 abut on the thick inner [i. e. toward the coelom) belt. 

 Gland-cells also occupy considerable areas internally at the 

 edge of the organ. The mIioIc structure of this organ there- 

 fore differs from mere labial folds of the vestibule, as mere 

 clearly seen in vertical sections (PI. VII. fig. 6), the densest 

 part of the cellular layer being toward the middle of the 

 ventral fold and thinning off dorsally and laterally. The 

 lip-organ, in short, is a highly differentiated ap[niratus, both 

 secretory and manipulative, for the tube-forniation and other 



