BRITISH NEMERTEANS, AND SOME NEW BRITISH ANNELIDS. 



427 



/• 



9- 



h. 

 h'. 

 h". 



J- 

 J- 

 k. 

 m. 

 m. 



71. 



o. 

 P- 



Superior ganglionic commissure. 



Inferior do. do. 



Ganglia. 



Superior lobe of ganglion. 



Inferior lobe of do. 



(Esophageal region. 



Alimentary cavity-proper. 



General stroma of cephalic region. 



Cephalic sacs. 



Ducts of cephalic sacs. 



Great lateral nerves. 



Proboscidian sheath. 



Dorsal blood-vessel. 



w. 



ov. 



Lateral blood-vessel. 



Lacuna? behind ganglia. 



Vascular meshes around the oesophageal 

 region. 



Larger vascular cavity at each side of the 

 sheath for the proboscis in front. 



Mouth. 



Constriction marking the junction of the oeso- 

 phageal region with the digestive cavity- 

 proper. 



Anus. 



Ovaries and their remains. 



Muscular ribbons of proboscis. 



Plate IV. 



Fig. 1. Transverse section, a short distance behind the tip of the snout of Ommatoplea alba, in front 

 of the ganglia, somewhat flattened from pressure. 1, 2, 3, 4, 5, 6, the various bands of 

 fibres described in the text ; e, longitudinal muscular fibres ; I, section of cephalic blood- 

 vessel ; m, section of cephalic sac. x 210 diameters. 



2. Transverse section of the body-wall of 0. alia, after hardening in spirit and mounting in 



chloride of calcium ; a, cutis, with its cells and areolae, somewhat compressed ; b, struc- 

 tureless basement-layer; c, circular muscular coat; d, longitudinal muscular coat; 

 e, delicate fibres pi'oceeding from the latter to the viscera. x 700 diameters. 



3. View of a portion of skin snipped from a living specimen, and submitted to moderate pres- 



sure, x 350 diameters. 

 ... 4. Longitudinal section of the anterior region of the proboscis of 0. alba. The same letters 

 are used as in fig. 4, PI. V. x 90 diameters. 



5. Transverse section through the anterior part of the cephalic ganglia, in a specimen which 



had been chloroformed and then immersed in strong alcohol, so as to protrude a small 

 portion of the proboscis. The inferior commissure (g) is not much stretched, but the 

 superior (/) is almost imperceptible ; j, oesophagus, x 55 diameters. In this and other 

 drawings, accuracy has been preferred to symmetry. 



6. Section of the snout in front of fig. 1, showing the channel for the proboscis (a), and the 



cephalic blood-vessels (I), just before they complete the arch. x 210 diameters. 



7. Elements as they escape from the fresh skin of the same animal ; a, granular cells ; b, mu- 



cous or gelatinous masses, having the appearance of oil-globules. x 350 diameters. 



8. Skin of O. alba, as seen near the tail of a small living specimen, under slight compression. 



x 350 diameters. 



9. Corpuscles of the proboscidian fluid ; a, minute nucleated cells and granules; b, spindle- 



shaped corpuscles. x 500 diameters. 

 ... 10. Stylet, from a lateral sac of the same species, showing a "wing" at base (from remains of 



globule), and an abnormal point. x 210 diameters. 

 ... 11. Discs of proboscidian fluid, from a specimen of Tetrastemma varicolor. x 350 diameters. 

 ... 12. Small gregariniform parasite, from the digestive cavity of Tetrastemma variegatum. x 210 



diameters. 

 ... 13. Proboscidian aperture in snout of 0. alba. x 210 diameters. 

 ... 14. Discs of proboscidian fluid from Tetrastemma variegatum. x 350 diameters. 



Plate V. 



Fig. 1. Transverse section through the cephalic ganglia of O. alba, in the line of the commissures, 

 the superior of which, from the flattening of the preparation, is shown very plainly ; 

 a, proboscis ; d, circular muscular fibres of the body-wall ; k, muscular and glandular 

 stroma of the region. x 90 diameters. 



