Oll tbe connective tissues and body cavities of the Nemerteans. Q 



skeletal sheath of the body. Its outer surface is pitted, the pits 

 being the seat of the deep lying epithelial glaud cells; on each side 

 of such a pit, a ridge or thorn of the membrane juts out between 

 these cells, serving as a point of insertion for the more superficial 

 gland-, and also for the supporting cells. The substance of the base- 

 ment membrane consists of branched cells and their fibres, imbedded 

 in an homogeneous intercellular substance (Fig. 9). The latter stains 

 very faintly, and encloses rounded or oval vacuoles (Vac) (filled in 

 life with a fluid?) of varied size and uneven distribution, which be- 

 come larger towards the inner surface of the membrane, and whose 

 contents do not stain. The cells imbedded in this homogeneous sub- 

 stance are comparatively more numerous anteriorly (i. e. towards the head) 

 than posteriorly. They are usually multipolar and branched, and usually 

 lie in a vacuole in the intercellular substance; the nucleus is seldom oval, 

 more frequently elongated, often irregular in outline, and stains deeply 

 (Figs. 9, 6 a— c). Especially characteristic for this tissue is the 

 structure of the cytoplasm around the nucleus, as is best seen after 

 the use of the Ehrlich-Biondi stain. The nucleus, namely, lies in, 

 or more frequently upon, the surface of an irregularly spherical or 

 elongate mass of cytoplasm, the latter filled with highly refractive 

 granules (Nutr), which stain a deep maroon color after the Ebuilich- 

 BiONDi stain and also intensely red after eosin ; usually these are nearly 

 uniform in size, but occasionally one or two granules or globules occur, 

 even exceeding the nucleus in size. Since the finely-alveolar, circum- 

 nuclear cytoplasm very seldom contains no granules, their presence 

 furnishes a good criterion for the occurrence of this tissue in other 

 parts of the body. These granules do not accompany, or but for a 

 short distance, the cell fibres. The cell is multi- or bipolar; its fine 

 branching fibres are of uniform diameter, but I have been unable to 

 determine whether they anastomose or not. Radial groups of such 

 fibres transverse the cutis, producing cone-shaped clusters, which are 

 placed at regular distances apart; each cluster is situated beneath 

 a ridge of the outer surface of the basement membrane, and its fibres 

 converge towards the point of the ridge (Figs. 1, 9). Since no muscle 

 nuclei accompany these radial fibres, and since, with the Ehrlich- 

 Biondi stain, they stain a rose-color, while the muscle fibres of the 

 outer circular layer stain a brown-red, they are certainly connective 

 tissue, and not muscle fibres. Hubrecht ('87) recognized the true 

 nature of these fibres, while Bürger ('90) supposed them to be radial 

 muscles, adding (1. c. p. 43): "In die Züge der radialen Musculatur 



