supporting lamella

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520 W. B. HARDY. retracts this region to such an extent that the epithelium is thrown into deep folds, and the free surfaces of the cells apposed. This ciliated zone forms only a narrow band. Between the bases of the ciliated cells are (2) numerous rounded and deeply-staining cells, which are more numerous the nearer the lip. Delicate processes may be sometimes seen passing from them to the surface, and they are probably sense-cells. Below these, and forming by far the greater portion of the epithelium, are strikingly characteristic palisade-like cells. Each has a very scanty and ill-stainiug protoplasm, which surrounds a large irregular vacuole occupying the bulk of the cell. Two nuclei, each with a small nucleolus, are usually present, and may be either close together about the middle of the cell, or one at either end. There is not the slightest evidence that the presence of these twin nuclei indicates cell division. At the lower edge of the ciliated zone conical cells appear between and rapidly replace the ciliated cells, while at the same time the deep-staining sense-cells disappear. Each of these conical cells resembles in its general appearance a gobletcell of an ordinary mucous membrane. We can, therefore, conveniently style the next region the goblet-cell zone. This embraces a considerable portion of the tentacle-bearing region. It is, however, impossible to reduce the relative dimensions of these various zones to numerical exactness because of the extreme extensibility of this portion of the animal. Each goblet-cell is, as its name implies, flask-shaped, and consists of an expanded part which stains lightly with picrocarmine (fig. 16) or osmic acid (fig. 15). The contents of this part are turbid from the presence of ill-defined, granular masses. The expanded portion of the flask is continued downwards into a tail, which contains a small nucleus embedded in deeply-staining granular protoplasm. The numerous and coarse granules of the basal portion stain deeply with osmic acid, and less so with picro-carmine. These cells are undoubtedly of the nature of gland-cells; and the wellformed basal granules may be regarded as the first stage in
HISTOLOGY AND DEVELOPMENT OF MYRIOTHELA PHRYGIA. 521 the elaboration of the secretion product which occupies the expanded portion of the cell. In the upper part of the gobletcell zone the endoderm is composed of goblet-cells lying wedged between the apices of palisade-like cells exactly resembling those occurring in the ciliated zone, except in the fact that they now abut on the free surface. When this portion is retracted the deep folds present the appearance in sagittal sections of long tubular glands, which, from the character of the abundant goblet-cells, closely simulate the crypts of the large intestine. In the middle and lower part of this region the endoderm is thrown up into low conical villi. These structures are characteristic of the whole of the endoderm with the exception of the part already described, that is in the neighbourhood of the mouth, and in the foot. They vary very much in length in the different regions of the animal, but are usually longest in the lower portion of the tentacle-bearing region, where they are long filiform structures, sometimes branched, and may measure - 3 to "5 mm. from base to apex. Generally speaking, the villi are not muscular, but in the goblet-cell region they appear to have a distinct muscular axis. Structure of a Villus from the Goblet-cell Zone. A section through the axis of one of these is shown in fig. 16. On the sides of each villus, and between their bases, we have the same arrangement of palisade-cells and goblet-cells as that described above. At the apex, however, are a group of cells presenting many new features. These I propose to call the apical cells, and they form not only the apex of the villus, but are also continued downwards as its muscular axis. Each apical cell has the following general structure. The protoplasm is abundant, and stains deeply, thus offering a marked contrast to the other cells of the villus. It is also turbid and opaque, but differs very much in this and in its behaviour with stains in different parts of the cell. In the muscular stem, however, the protoplasm is always
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