. The embryology and metamorphosis of the Macroura . rizontal sections (Fig. l(i2-lC5). Fig. UJS which is from auembryo a little more advanced, shows that the endoderm is rising from the nervous cord near itspoint of llexiiie, into a transverse vertical fold. Simultaneously with the upward growth of thisventral foltl, two dorsal longitudinal folds grow downward, aiid-linally unite with the ventral foldantl with each other, thus coiistrictiug off from the alimentary tract two lateral pouches, the pri-iL-ary lobes of the liver. The folils grow forward and the constriction i>roceeds gradually
. The embryology and metamorphosis of the Macroura . rizontal sections (Fig. l(i2-lC5). Fig. UJS which is from auembryo a little more advanced, shows that the endoderm is rising from the nervous cord near itspoint of llexiiie, into a transverse vertical fold. Simultaneously with the upward growth of thisventral foltl, two dorsal longitudinal folds grow downward, aiid-linally unite with the ventral foldantl with each other, thus coiistrictiug off from the alimentary tract two lateral pouches, the pri-iL-ary lobes of the liver. The folils grow forward and the constriction i>roceeds gradually withthe growth of the embryo. This process is illustrated by the diagrams (Fig. 1) which were drawnfrom an embryo near the point of hatching. The histology of the endoderm as shown in Fig. 173,is the same as in the previous stag^. The cells are inismatic, and tlie nucleus .spherical,and, as in all stages, tilled with numerous nucleoli or chromatin balls. The cell walls are verydelicate and the protoplasm often contains large 9S> Fic;..>. — Seiiii<IiaKraniniatic representation of the alimentary imet and iin ;i|i|ien<la):ea in thelirat larva of Atiihrim taiilnii. The niidille lin^ of Ibe body i» also shown. , foreRut. gg 1-3,secondary Iobiili« of posliio lateral lobe of luidgnt; //S, hindgut; iiiy. uiidyul; ing 1-3, an-terior, lateral, and post«ro-lateral divisions of luidgut; nio, mouth. 41G MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. Wandering cells still occur in all parts of the yolk, tbough in far less abundance than inearlier stages. We find numbers of them moving toward the periphery, or next the body wall totake part in forming the endoderm. The epiblaist is conspicuous in Fig. 1G8 just in front of theoptic lobes. This corresponds in position with the dorsal plate (Fig. 153 dj).), and is i)robably aremnant of it. The small clusters of cells beneath it and the degenerative products which occurnear them, probably also represent
Size: 1912px × 1306px
Photo credit: © Reading Room 2020 / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookauthor, bookcentury1800, bookdecade1890, booksubjectcrustacea
