On the connective tissues and body c rvities of the Nemertoans. \ 1 



the Metauomertiiii, the muscle fibres are arranged iu muscle buudles. 

 In Carinella, iu the longitudinal muscle layer, a varying number 

 (averaging about 15) of muscle fibres produce a muscle bundle, which 

 is round on cross section. Between such muscle bundles, and en- 

 veloping each bundle, as well as its separate fibres, is situated the 

 connective tissue under discussion, being in direct connection with 

 the intermuscular tissue of the other muscular layers, and bearing the 

 characteristic granulated cells (Fig. 4). The fibres of these cells 

 produce a thin sheath around each muscle bundle, while between such 

 sheaths, and between the individual muscle fibres, mainly homogene- 

 ous intercellular substance is situated. But this tissue apparently 

 does not envelop that portion of the muscle fibre, which faces the 

 cavity of the muscle bundle. This cavity remains on preparations as 

 a rule colorless, and without evidence of structure, except that at 

 intervals a few connective tissue fibres cross it; on a few sections I 

 found a finely granular, faintly staining mass, which would re- 

 present the homogeneous fluid which probably fills the cavity in life 

 (Fig. 4 Fl). 



2) The mesenchym tissue. In the mature worm, the body 

 cavity is much more reduced than in the specimen of Cerehratulus 

 examined. But even in the mature Carinella, a body cavity may still 

 be found in the posterior region of the trunk (behind the proboscis), 

 around the lateral bloodvessels and between the gonads (Fig. 2 B.C)\ 

 dorsally and ventrally, however, the intestine is in contact with the 

 longitudinal muscle layer. The mesenchym cells (Figs. 3, 7 Mes) 

 found in this body cavity are usually elongate and bipolar, with flat- 

 tened, irregular, anastomosing fibres. Neither iu Carinella^ nor in the 

 other species, do the mesenchym cells produce cell membranes nor 

 intercellular substance, but are always surrounded by the fluid of the 

 body cavity. The nucleus, oval or elongated in form, and frequently 

 presenting evidences of amitotic division, lies, as a rule, in or upon 

 a deeply staining granular mass, similar to that of the cells of the 

 last described tissue; a small percentage of the mesenchym cells are 

 apparently devoid of the granular mass. One or two nucleoli are 

 usually present, and division of the nucleolus is figured in Fig. 7. 

 Finally, a small number of free floating cells, also characterized by 

 the granular mass, and from which the fibres have become detached, 

 are situated in the body cavity. There is found in the body cavity, 

 between these cells, a faintly staining, finely granular mass; these 

 granules would represent sections of the terminal fibres of the 



