On the connective tissues und body cavities of the Nemerteans. 21 



as in Cerehrattdus, but in the muscular layers of the body wall it is 

 somewhat diminished in amount, owing to the presence of the tissue 

 there, next to be described. And since in this species of Linens, no 

 mesenchymic pseudoepithelium lines the inner surface of the inner 

 longitudinal muscle layer, this tissue forms a membrane between this 

 muscle layer and the intestine. The nucleus is oval or sjjindle-shaped, 

 deeply staining, and lies in a membraneless mass of cytoplasm, from 

 which branching fibres radiate into the homogeneous intercellular sub- 

 stance ; this intercellular substance stains with haematoxylin , and 

 produces membranes and sheaths around and between the muscle bundles. 

 2) Pigmented connective tissue without inter- 

 cellular substance, in the body wall. This is characteristic for 

 Lineus, under the genera examined. There is a deep cuticular gland- 

 cell layer, extending from the body epithelium to the circular muscle 

 layer of the body wall, or even penetrating at intervals the inner 

 longitudinal muscle layer, its cells lying among the fibres of the 

 epithelial (so-called) and those of the outer longitudinal muscle layer. 

 The majority of the gland cells are rhabdite producing cells (a large 

 number of rhabdites being produced by a single cell), and become 

 less numerous posteriorly; there are also at intervals eosin- and 

 haematoxylin-staining gland cells, which produce a slimy secretion. 

 Around these gland cells and the adjacent muscle fibres, lies the 

 pigmented connective tissue, in this way occupying most of the space 

 not filled by the previously described tissue. It is more abundant, 

 and more heavily pigmented on the dorsal side of the worm, than 

 elsewhere. Its cells (Fig. 24) are membraneless, and not united by 

 an intercellular substance , and have a great resemblance to the 

 interstitial cells in the body epithelium of Stichostemma. The nucleus 

 is oval, and its small chromatin granules are pretty evenly distributed. 

 A multipolar mass of cytoplasm envelops the nucleus, and from this 

 mass, long and immeasurably fine, branching fibres are giveu off, 

 which anastomose with those of neighbouring cells. Greenish-yellow 

 pigment granules, of unequal size, are distributed along the fibres, or 

 amassed around the nucleus; a fixing reagent containing OsO^ pro- 

 duces a globular form of these granules, which might prove that the 

 pigment is of a fluid consistency in life. Pigmented fibres of these 

 cells pass also through the basement membrane, and between the cells 

 of the body epithelium; but none of their nuclei are found in the 

 latter. The only pigment found in the body epithelium is contained 

 in these fibres. Fibres of these cells also penetrate between the 



