THE "PYLORIC GLAND" OF THE ASCIDIAN BOTRYLLUS—AN ORGAN OF EXCRETION?

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Abstract
1. There are in Botryllus two sorts of terminations to the tubes that compose the pyloric gland, bladder-like ampullæ and long straight blind tubes—the latter we have called rectal tubules because in many cases they extend to the region of the rectum. 2. The ducts and ampullæ of Botryllus as well as Ascidia, Styela, Molgula, Perophora, Clavelina and Amaroecium are lined by cells bearing long whip-like flagella, the ends of which are directed toward the mouth of the duct. 3. Many of the rectal tubules have a termination difficult to interpret. This has the appearance, in most cases, of a cup-like depression in the end of the tube which seems to form a communication between the blood cavity and the lumen of the tube. In no case, however, could such a communication be demonstrated. 4. The direction in which the free ends of the flagella point indicates that the contents of the lumen pass toward the stomach and therefore the function of the organ is secretory rather than that of absorption. 5. Part of this secretion is probably found in the minute yellow globules found in the cells of the ducts and ampullæ. If these yellow globules represent a secretion, this is soluble in water and does not form masses in the lumen of the tube as in Microcosmus and Styela. 6. Bismarck brown and neutral red are concentrated in the lumen of the organ in the form of a liquid while the indigo carmin is found concentrated in solid form in the gland of Styela. 7. In the tunicates in general no special kidney of excretion has been recognized. Although the gland in question may have other functions also, yet its structure and properties seem to indicate that it is the kidney of excretion of the tunicates, and is in turn homologous to the vertebrate liver.

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