PLATE VIII. 



Figs. 1, 2. Pterosoma plana, Less. After Lesson, supposed by Moseley to represent a species of Pelago- 



nemertes. 



Fit;, i. Seen from above. 

 Fig. 2. Seen from below. 



Fig. 3. Pelagonemertes rollestoni, II. N. M. A transverse section, supposed to be not quite vertical to 

 the longitudinal body axis, so that to the right one of the digestive, to the left one of the 

 generative cseca was touched in the section. Ep, external epithelial layer; B, basement 

 membrane; LM, layer of longitudinal muscles; J, intestine and its branching diverticula; 

 N, longitudinal nerve-stem; bl, two lateral blood-vessels; Gc, external opening of the 

 generative caecum; P.S.C, the cavity of the proboscidian sheath; Ps, the wall of that 

 cavity. All the internal organs are surrounded by and imbedded in a wholly continuous 

 gelatinous ground substance, in which a few cells and numerous fibres can be detected, 

 and which has more strongly imbibed the staining reagent in the immediate vicinity of 

 the different organs and tissues that traverse it. 



Fig. 4. Pelagonemertes rollestoni, H. N. M. A horizontal aspect of the muscular layers of the body- 

 wall, from a preparation made of the fresh animal by Professor Moseley. Im, the 

 longitudinal muscles ; em, the sparse circular muscular fibres, external to the foregoing ; 

 dr, granular patches, eventually glandular structures; ct, the gelatinous connective tissue 

 visible between the muscle fibres. 



Fig. 5. Pelagonemertes rollestoni, H. N. M. A transverse section of what most probably corresponds 

 to one of the granular patches of fig. 4, furnishing arguments for looking upon the latter 

 as glandular. " A central lumen (or fibre 1 ?), with nuclei surrounding it can be detected. 



Fig. C. Pelagonemertes rollestoni, H. N. M. The longitudinal nerve-stem iv", in transverse section. 

 A branch n gives off smaller nerve-twigs n' and n". Nuclei are imbedded in the fibrous 

 nerve substance. The gelatinous connective tissue is more deeply stained all round, and 

 at ff has a distinctly fibrous appearance. 



Fig. 7. Pelagonemertes rollestoni, H. N. M. The posterior region of the proboscis, in transverse 

 section. II, the longitudinal muscular fibres, externally invested by a basement mem- 

 brane ; E, the epithelium, of which no details could be made out. 



Fig. 8. Pelagonemertes rollestoni, H. N. M. An empty genital caecum, in transverse section. In 

 the lower narrower part the epithelium is high and very distinct and a couple of epi- 

 thelium-cells are becoming converted into ova, ov. N, the nerve-stem; hi, the blood- 

 vessel ; Gc, the empty cavity ; etc, connective tissue cells in the gelatinous ground- 

 sabstance ; /, fibrous tracks in the same. 



Fig. 9. Pelagont mertes rollestoni, H. N. M. Isolated transversely striated cells from the wall of the 



cavity, Gc, in fig. 8. 



Fig. 10. Pelagonemertes rollestoni, H. N. M. A young ovum. 



Fig. 11. Pelagonemertes rollestoni, H. N. M. A larger ovum, surrounded by its follicle cells (cf. 

 fig. 3). No distinct nucleolus, but numerous chromatic granules inside the nucleus. 



Fig. 12. Pelagonemertes rollestoni, H. N. M. Portion of the proboscidian sheath, in transverse section, 

 under higher power. B, the inner homogeneous limiting membrane; Im, longitudinal; 

 cm, circular muscular layer; ct, the outer sheet of the gelatinous tissue immediately 

 applied against the muscles and again more deeply stained. 



Fig. 13. Pelagom mertes rollestoni, H. N. M. Portion of the outer layers of the body-wall, under still 

 higher power. The external cellular epithelium has not been represented. B, the thick 

 basement membrane, below this epithelium, traversed radially by apparent glandular ducts 

 («•/'. figs. 4, 5); B', a deeper portion of the same, less affected by the staining solution, and 

 carrying connective tissue cells; cm, isolated circular, LM, thicker bundles of longitu- 

 dinal muscular fibres ; dr, probable glandular ducts in the gelatinous ground-substance 

 penetrating through the muscles to the exterior. 



