. 1 mm Text-fig. 6. Transverse section through a gastrozooid in the basal region, ec = ectoderm, en = endoderm, mes = mesogloea, v = villi, cut at various angles. Turning now to the basal region of the gastrozooid, we find a more complicated organization of the endoderm. The most conspicuous features are the villi. These are finger-like projections from the lining of the zooid, consisting of endoderm cells covering a central core of mesogloea (Text-fig. 6; PI. XXVII, fig. 6); the ectoderm is not involved. The villi can be seen through the transparent wall of the zooid (Text-fig. 4). The endode
. 1 mm Text-fig. 6. Transverse section through a gastrozooid in the basal region, ec = ectoderm, en = endoderm, mes = mesogloea, v = villi, cut at various angles. Turning now to the basal region of the gastrozooid, we find a more complicated organization of the endoderm. The most conspicuous features are the villi. These are finger-like projections from the lining of the zooid, consisting of endoderm cells covering a central core of mesogloea (Text-fig. 6; PI. XXVII, fig. 6); the ectoderm is not involved. The villi can be seen through the transparent wall of the zooid (Text-fig. 4). The endodermal cells of the villi are probably all of one type; they are quite clearly active in intra- cellular digestion. In certain specimens, which had been feeding shortly before fixation, the enteron is filled with a mixture of partly-digested flesh, pigment, both dispersed and in aggregates, and nematocysts, discharged and undischarged. The same objects have been identified in vacuoles in the endoderm cells of the villi, and it may therefore be stated with confidence that these cells engulf whole particles of food, and enclose them in digestive vacuoles. A variety of stages in the breakdown of food can be found amongst the vacuoles. The pigment in the food is probably melanin, guanin or some other pigment originating from the dermal chromatophores and iridocytes of the captured fish. Part of it may, however, derive from broken down haemoglobin originating in the blood of the fish. The pigment evidently resists digestion in the vacuoles fairly successfully, for the cells of the villi nearly always contain some, whether feeding has taken place recently or not. Presumably it is eventually ejected, and some of the dispersed
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Keywords: ., bookcentury1900, booksubjectocean, booksubjectscientificexpediti
