. Text-book of embryology. Embryology. 636 mVEETEBRATA chap. mesoderm. A posterior mass is the rudiment of the elaeoblast, a protuberant mass of fatty globules which probably represents the last vestige of the lost larval tail. The pharyngeal cavity then appears in the centre of the median portion of the endodermic mass. It is nearly divided into two by a median dorsal infolding, the rudiment of the adult "; The cloacal cavity appears as a median invagina- tion of ectoderm, and unites with the pharynx at the sides of this so-called " ; The nervous system separates
. Text-book of embryology. Embryology. 636 mVEETEBRATA chap. mesoderm. A posterior mass is the rudiment of the elaeoblast, a protuberant mass of fatty globules which probably represents the last vestige of the lost larval tail. The pharyngeal cavity then appears in the centre of the median portion of the endodermic mass. It is nearly divided into two by a median dorsal infolding, the rudiment of the adult "; The cloacal cavity appears as a median invagina- tion of ectoderm, and unites with the pharynx at the sides of this so-called " ; The nervous system separates from the ectoderm and becomes hollowed out, showing a transient indication of division into three. Fig. 462.—The embryo of Salpa fusifarmis attached to the maternal placenta, seen from the .side. (After Salensky.) a, anus: at, atrial opening; , dorsal lamina (remnant of dorsal wall of pharynx); el, elaeoblast; endst, endostyle; //, heart; , blood-forming organ in the placenta; hyp, hypophysial canal; vtlt, intestine ; m, mouth ; , circular bands of muscle ; , nerve ganglion ; oes, oesophagus ; per, pericardium; pi, placenta. chambers, which have been compared to the three brain-vesicles of the embryos of higher Vertebrates {, Fig. 464). The neural tube becomes connected with the pharynx close to where the mouth is formed as an invagination. The mesodermic mass on each side gives rise to the characteristic hoop-like muscles which are the adult organs of locomotion. The elaeoblast is now gradually absorbed, the embryo wrenches itself loose, breaking off the placental knob,and carrying away with it this portion of the maternal tissues embedded in its body, where it is gradually absorbed, though its remains can be recognized for a long time. In Dolioluni, the other well-known genus of Thaliaceae, the egg is shed into the sea, and its early development seems to resemble that. Please note that these images are extracted from scanned page images that may have b
Size: 1906px × 1311px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1910, bookpubli, booksubjectembryology
