. Text-book of embryology. Embryology. 124 INVEETEBEATA CHAP. discovered, so that these larvae could be reared in large numbers through their metamorphosis, under experimental conditions, and if each stage in this change were thoroughly examined by sections, then a flood of much-needed light would be thrown on this period of Nemertine development. If the reader has followed the description so far given it will be evident that when all four amniotic invaginations completely coalesce they must cut the larva into an upper and a lower half. This is just what happens; and the lower and inner half,
. Text-book of embryology. Embryology. 124 INVEETEBEATA CHAP. discovered, so that these larvae could be reared in large numbers through their metamorphosis, under experimental conditions, and if each stage in this change were thoroughly examined by sections, then a flood of much-needed light would be thrown on this period of Nemertine development. If the reader has followed the description so far given it will be evident that when all four amniotic invaginations completely coalesce they must cut the larva into an upper and a lower half. This is just what happens; and the lower and inner half, invested by the coalesced floors of the amniotic invaginations, and containing the alimentary canal, drops to the bottom of the sea and commences life as a young. Fig. 99.—Two stages in the development of the Nemertine rudiment within the Pilidium, viewed from above. (After Salensky.) , cephalic .slits ; o, mouth ; , oesophageal pockets. Nemertine worm. The upper half consisting of the larval ectoderm, including the prototroch, lappets, and apical sense organ, and bounded inside by the coalesced roofs of the invaginations or amniotic invest- ment, continues to swim about for a little time before its energies are exhausted, and then it dies. EXPERIMENTAL WORK. E. B. Wilson and his pupils Yatsu and Zeleny have performed a most interesting series of experiments on the eggs and embryos of Gerebratulus, the general results of which may be shortly recounted here. The unfertilized egg was cut or shaken into fragments. If this be done before the membrane of the nucleus has disappeared, and if sperm be added to the fragments, only the fragment in which the. 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 MacBride, E. W. (Ernest William), 1866-1940; Kerr, John Graham, 1869-; Heape, Walter, 1855-1929. London
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Keywords: ., bookcentury1900, bookdecade1910, bookpubli, booksubjectembryology
