On the Structure of the Excretory Organs of Amphioxus. Part 2.—The ...

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194 EDWIN S. GOODRICH. although sometimes the epithelium seems to stretch over the base of the solenocyte tubes for a considerable way. The coelomic epithelium is not continuous with the wall of the canal at the tip of the diverticula, but often can be seen in sections to end with a free and jagged edge. Over the region where the solenocytes occur there is a gap in the coelomic epithelium, so that coelomic fluid freely bathes the solenocyte tubes (figs. 2, 3). That the space in which lie these tubes, and even the deep pockets described above (p. 193), communicate with the coalom is evident in specimens injected with Indian ink. Since no epithelium covers the solenocytes their true relation to the coalom cannot be made out for certain in •the adult. Without going into the question of their development in this paper, I may say that a careful examination of M. Legros's excellent preparations has convinced me that in the very earliest stages of its development the whole rudiment of the nephridium and solenocytes lies enclosed between the coelomic epithelium and the atrial wall. There is nothing unusual in the solenocytes coming into secondary contact with the coelomic fluid. We know that in the Actinotrocha larva the nephridium pierces the wall of the preseptal htomocoel, and the solenocytes project freely in the blood (8). In many Polychsetes also the nephridium passes through the coelomic epithelium and the solenocytes lie naked in the coelomic fluid (6). To sum up the chieE points in this contribution :—The careful examination of the nephridia in sections and in the living state shows that they have no internal opening. The tubes of the solenocytes pierce the wall of the nephridial canal, and open into its lumen. The flagellum passes down the tube into the lumen. The solenocytes are attached to the wall of the bloodvessels, which expand in this region, and may surround the canal. Both the bloodvessels and the nephridial canal are covered by the coelomic epithelium, being situated between it and the atrial wall. Over that region which is occupied by the solenocytes there is a gap in
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On the Structure of the Excretory Organs of Amphioxus. Part 2.—The ...

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