In addition to these, the ciliated ventral cup below the disc of many Melicertidae secretes a viscid substance (Fig. 116, _p_); and possibly the whole surface of the body is secretory in those species of this group, and of the Flosculariidae, whose tube (Fig. 115, A) is uniform and not made of pellets. In several other species belonging to Bdelloida and Ploima-Illoricata a viscid secretion of the surface of the body renders it "sordid" with adherent particles of dirt. When the secretion takes the form of a tube, the body can be wholly withdrawn into it by the contraction of the foot. In _Floscularia_, _Stephanoceros_, and _Conochilus_ the tube is hyaline and thin-walled; in _Oecistes_ and _Cephalosiphon_ it is more or less floccose; and in _Limnias_ it is thin, firm, and annulated. In _Melicerta_ and some species of _Oecistes_ the tube thus secreted by {206}the body is only formed in a very young state. In _M. janus_ and _M. pilula_ it is increased by the successive deposition of ovoid faecal pellets on to the rim. In _M. ringens_ (Fig. 116) and _M. conifera_ pellets are formed of the excess of the food particles brought to the disc by the ciliary current; they are carried through the gutters on either side of the projecting ventral lip or "chin" into the ciliated glandular cup on that side of the head. Here, as they revolve, they are cemented together into a pellet which is spheroidal in the former species, cylindro-conoidal with a basal hollow like a rifle-bullet in the latter. After a pellet is completed the animal stoops down and deposits it on the edge of the tube. This may easily be verified by furnishing a young _Melicerta_ with water containing solid particles of carmine. _M. tubicolaria_ forms a thick tube which is laminated, the laminae being directed upwards and outwards, and having diatom shells, etc., between the layers. In this case we have observed that the faeces are pellucid, and sometimes are so ejected as to lie in a sheet against the funnel-shaped mouth of the tube, and we are inclined to believe that the tube itself is formed altogether in this way. A similar process probably occurs in _Oecistes crystallinus_ and _Oe. umbella_. The _muscles_ are simple elongated fibres, usually having near the middle a mass of granular protoplasm containing a nucleus; they may be smooth or striated. The principal muscles of the body are conspicuously striated in many active free-swimming forms (_Pedalion_, _Synchaeta_, _Pterodina_, _Triarthra_).