The Journal of experimental zoology . aciliated epithelium (fig. 4:, A). At its junction with the inter-secting vessels, I have always found a flat semicircle of whatseems to be smooth muscle cells (fig. 4, B). The location ofthe ciliary surface of the papilla and the muscle at its base areintimately concerned with the collection and movement of thefood. By removing a part of the test and branchial sac, it is easyto observe with a binocular microscope the function of thepapillae. Food particles which are filtered by the meshes of THE JOURNAL OF EXPERIMENTAL ZOOLOGV, VOL. 25, NO. 1 242 SELIG HE
The Journal of experimental zoology . aciliated epithelium (fig. 4:, A). At its junction with the inter-secting vessels, I have always found a flat semicircle of whatseems to be smooth muscle cells (fig. 4, B). The location ofthe ciliary surface of the papilla and the muscle at its base areintimately concerned with the collection and movement of thefood. By removing a part of the test and branchial sac, it is easyto observe with a binocular microscope the function of thepapillae. Food particles which are filtered by the meshes of THE JOURNAL OF EXPERIMENTAL ZOOLOGV, VOL. 25, NO. 1 242 SELIG HECHT the branchial sac are rapidly lashed to the tips of the papillaeby their ventral cilia. Here they are caught by the mucus, andincorporated into the thread of food which is passing across thebranchial sac. This cord of mucus and food is transported bythe papillae. Waves of contraction bring two rows of papillaetogether, and by the action of the cilia the food cord is passedfrom one row to the next, until it reaches the Fig. 4 Papilla of the branchial sac. A, median section; B, section at the baseof the papilla. The mechanism for these papillary movements is probablylocal, because touching a papilla with a glass rod causes a con-traction to appear. This would indicate that the waves are theresult of a series of stimulations of the papillae by the contactof the food mass. The food as it enters the oesophagus is in the shape of a cord,and in this manner it is passed along the digestive tube. Withthe food also goes the mucus. Although the food is digestedand absorbed, the mucus is probably not affected at all. When PHYSIOLOGY OF ASCIDIA ATRA LESUEUR 243 the feces come out in neat, flat, oblong packets, they are incasedin a thin layer of gelatinous material, which is probably themucus. The presence of the gelatinous covering of the fecesis best seen in animals which have been in the laboratory forsome days. In such cases the feces contain but little excrement,and are
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Keywords: ., bookauthorwi, bookcentury1900, bookdecade1910, booksubjectzoology
