36 THOS. H. MONTGOMERY, 



found, and which is bounded by non-continuous pseudoepithelia of 

 mesenchym cells ; and in males of Stichostemma, such pseudoepithelial 

 linings are also found. Only in Tetrastemma is this body cavity 

 wholly obliterated. But in theMetanemertini there is no coelomic 

 cavity, such as Salensky ('84) has described for Monopora, in the 

 connective tissue sheath, which encloses the gonads, nerve chords, and 

 lateral vessels; since the (probably archicoelic) body cavity of this 

 group, lies between this sheath and the body muscular wall. 



8) Wherever a body cavity is present, it always encloses mesen- 

 chym cells. These are typically bipolar, but sometimes multipolar, 

 membraneless cells, with branching, flattened fibres, and without inter- 

 cellular substance of their own production, situated in the fluid of the 

 body cavity; I have applied the term mesenchym to them, because 

 they resemble, more than any other connective tissue elements found 

 in the mature worm, the true embryonal mesenchym. 



9) The gonadal membrane is, apparently always, a product of 

 the connective tissue cells with dense intercellular substance; the 

 genital cells are either derivatives of cells of this tissue (in Lineus 

 and the Me taneraertini), or of mesenchym cells (in Carinella and 

 perhaps Cerebratulus). 



10) I have been able to demonstrate in Carinella a liquid con- 

 tained within the muscle bundles. 



11) In the adult Nemerteau , amitotic division stages in the 

 mesenchym cells are frequent; but no cell divisions occur in the other 

 connective tissues, except those true mitotic divisions in the tissue 

 with intercellular substance, which give rise to the genital cells. 



12) Having had no embryonal material at my disposal, I have 

 been unable to pursue studies on the histogenesis of these tissues ; 

 but having had opportunity to compare the different connective tissues 

 in representatives of the Proto-, Meta- and Heteronemertini, 

 I would endeavour to explain their relationships as follows. The 

 parenchym diflers from the other tissues in structure, in that its cells 

 possess membranes, have no intercellular substance nor extraneous 

 fibres, and further, in that the cell is largely filled with a structure- 

 less liquid. The diflerentiation of the parenchym cell may be called 

 endoplastic, to adopt the terminology of Lankester ('80j, while 

 the cellular differentiations of the other connective tissues are ecto- 

 pias tic; and since both have very diflerent physiological functions 

 I would class the parenchym tissue by itself, in contrast to the others. 

 Of the other tissues, the mesenchym is structurally the most primi- 



