On the connective tissues and body cavities of the Nemerteans. 17 



mesenchym cells are produced. In other words, the free-floating 

 mesenchym cells of the body cavity are produced, probably, l)y the 

 amitotic division of the large cells of the outer pseudocpithelium. 



It is very probable that the genital cells are of mesenchyniatic 

 origin, since no connective tissue with intercellular substance — the 

 only other tissue from which the genital cells originate in the Nemer- 

 teans, is found within the inner longitudinal muscle layer of the body 

 wall (i. e. in the region of the gonads); but I could make no 

 observations to determine this point, since neither gonads nor genital 

 products were difi'erentiated in the specimen examined. 



In this species the mesenchym differs markedly from the connec- 

 tive tissue with intercellular substance, whereas in the other species 

 examined these two tissues may be very similar. 



I would note the close structural resemblance between the various 

 states of the mesenchym cells in Cerehratulus ^ and those in the 

 mesenchym cells of Bhodope, according to Böhmig ('93). 



In the caudicle the body cavity is much reduced, owing to the 

 greater size of the mesenchym cells in this region, and their denser 

 grouping (Fig. 16 Mes). Here they are closely massed between the 

 fibres of the outer, and of the inner longitudinal muscle layer, as well 

 as between the latter and the intestine. Further, they build a dense 

 layer, about 4 to 6 cells deep, around the lateral nerve chord, since 

 in the caudicle the chords are not enveloped by ganglion cells! — a 

 condition heretofore undescribed in any micrureau Heteronemertean 

 (Fig. 18). I have not found any ganglion cells in the caudicle, com- 

 parable to those found in the anterior portion of the nerve chords; 

 and while in the last named portions, the ganglion cells are limited 

 in their occurrence to the dorsal and ventral aspects of the chord, 

 the mesenchym cells in the caudicle produce a thick, semicircular 

 layer of cells, enveloping the chord on its outer surface, as well as 

 dorsally and ventrally. Further, there is no gradual intergradation 

 between the mesenchym cells behind, and the ganglion cells in front; 

 but in the space of a few thin sections (5 i.i\ the latter become en- 

 tirely replaced by the former. The grouping of mesenchym cells 

 around the nerve chord becomes denser towards the distal end of 

 the caudicle. The mesenchym cells of the caudicle are larger than 

 those of the anterior portions of the body cavity, and the nucleus 

 also is larger, but with a proportionately smaller amount of chromatin. 

 They also have shorter fibres, being somewhat star-shaped, and are 

 much more densely massed together. Many of the cells are evidently 



Zool. Jahrb. X. Abth. f. Morph 



