The collar (called the peristome by Cohn) is evidently formed, like the valve, by an inward projection of the walls of the bladder.  The cells composing the outer surface, or that facing the valve, have rather thick walls, are of a brownish colour, minute, very numerous, and elongated; the lower ones being divided into two by vertical partitions.  The whole presents a complex and elegant appearance.  The cells forming the inner surface are continuous with those over the whole inner surface of the bladder.  The space be- [page 402] tween the inner and outer surface consists of coarse cellular tissue (fig. 20).  The inner side is thickly covered with delicate bifid processes, hereafter to be described.  The collar is thus made thick; and it is rigid, so that it retains the same outline whether the bladder contains little or much air and water.  This is of great importance, as otherwise the thin and flexible valve would be liable to be distorted, and in this case would not act properly.

Altogether the entrance into the bladder, formed by the transparent valve, with its four obliquely projecting bristles, its numerous diversely shaped glands, surrounded by the collar, bearing glands on the inside and bristles on the outside, together with the bristles borne by the antennae, presents an extraordinarily complex appearance when viewed under the microscope.

We will now consider the internal structure of the bladder.  The whole inner surface, with the exception of the valve, is seen under a moderately high power to be covered with a serried mass of processes (fig. 21).  Each of these consists of four divergent arms; whence their name of quadrifid processes.  They arise from small angular cells, at the junctions of the angles of the larger cells which form the interior of the bladder.  The middle part of the upper surface of these small cells projects a little, and then contracts into a very short and narrow footstalk which bears the four arms (fig. 22.).  Of these, two are long, but often of not quite equal length, and project obliquely inwards and towards the posterior end of the bladder.  The two others are much shorter, and project at a smaller angle, that is, are more nearly horizontal, and are directed towards the anterior end of the bladder.  These arms are only moderately sharp; they are composed of ex-[page 403] tremely thin transparent membrane, so that they can be bent or doubled in any direction without being broken.  They are lined with a delicate layer of protoplasm, as is likewise the short conical projection from which they arise.  Each arm generally (but not invariably) contains a minute, faintly brown particle, either rounded or more commonly elongated, which exhibits incessant Brownian movements.  These par-

Fig. 21. (Utricularia neglecta.) Small portion of inside of bladder, much enlarged, showing quadrifid processes.

Fig. 22. (Utricularia neglecta.) One of the quadrifid processes greatly enlarged.