. Outlines of zoology. Zoology. Fig. 137.—Diagrams of Insect embryo.—After Korschelt and Heider. A tranverse section before the union of the amnion folds, and a longitudinal median section after the union of the folds, a., Anterior end of blastoderm; p., posterior end of blastoderm; , in the left-hand figure, the beginning of the amnion fold ; am., amnion ; , amniotic cavity ; s.\ serosa ; ectoderm ; //., lower germinal layer ; y., yolk. The amniotic cavity marks the future ventral region of the embryo, so that the yolk mass is dorsal. may be left behind in the central yolk to fo
. Outlines of zoology. Zoology. Fig. 137.—Diagrams of Insect embryo.—After Korschelt and Heider. A tranverse section before the union of the amnion folds, and a longitudinal median section after the union of the folds, a., Anterior end of blastoderm; p., posterior end of blastoderm; , in the left-hand figure, the beginning of the amnion fold ; am., amnion ; , amniotic cavity ; s.\ serosa ; ectoderm ; //., lower germinal layer ; y., yolk. The amniotic cavity marks the future ventral region of the embryo, so that the yolk mass is dorsal. may be left behind in the central yolk to form the yolk nuclei, or, what is probably the more primitive condition, these are formed by subse- quent immigration from the blastoderm. The next process is the appearance of differentiation among the similar cells of the blastoderm. Over a special area—the ventral plate—(cf. Astacus) the cells increase in number and become cylindrical in shape ; over the rest of the egg the cells flatten out and become much thinner. In the middle of the ventral plate a slight groove is formed by rapid multiplication of the cylindrical cells. This represents the disguised gastrulation, the open roof of the groove being the much elongated blastopore. The surrounding cylindrical cells unite over this open roof,. 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 Thomson, J. Arthur (John Arthur), 1861-1933. Edinburgh, Glasgow and London, H. Frowde and Hodder & Stoughton
Size: 1142px × 2188px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookauthorth, bookcentury1800, bookdecade1890, booksubjectzoology
