. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. No. 3.] THE PHARYNX OF ALLOLOBOPHORA. 15. The tip of the regenerated part was destroyed with a hot needle on February 2, and the worm was killed on February 17. Both figures show the diverticulum which has grown out from the walls of the oesophagus about to open to the exterior by fusion with the ectodermal pit; and a comparison with the sections in the same neighborhood shows that these two repre- sent the nearest approach of ectoderm and endoderm to be found in the two specimens. The walls of the pharynx and its musculatur
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. No. 3.] THE PHARYNX OF ALLOLOBOPHORA. 15. The tip of the regenerated part was destroyed with a hot needle on February 2, and the worm was killed on February 17. Both figures show the diverticulum which has grown out from the walls of the oesophagus about to open to the exterior by fusion with the ectodermal pit; and a comparison with the sections in the same neighborhood shows that these two repre- sent the nearest approach of ectoderm and endoderm to be found in the two specimens. The walls of the pharynx and its musculature, especially on the dorsal side, are well developed. In both worms a nerve cord and a cerebral ganglion have been formed, the latter for the second time. Owing: to the slight ob- o o liqueness of the section, as shown in Fig. 2, the nerve cord is cut for only a part of its length. The muscles of the body wall have be- gun to differentiate and there are clear indications of metamerism. All of the worms used in this set of experiments, as well as all those in a later set made to test these results, present a similar condition of things. From these results we must conclude that the lining of the pharynx is regenerated from the endoderm, while the new ecto- derm turns in for a very short distance to meet the pharynx and form the mouth. The objection may be raised that the possibility of a later pushing in of the ectoderm to form the ultimate lining of the pharynx is in no way removed. But there is no evidence for such an occurrence and, even if it did take place, the fact remains that the musculature of the pharynx develops around an endodermal tube, as my experiments have shown, while in. FIG. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Marine Biological Laboratory (Woods Hole, Mass. ); Marine Biologic
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
