The development of the human body; a manual of human embryology . proceed with that regularitywhich marks the segmentation of Amphioxus or an amphi-bian, but while at first it divides into two slightly unequalcells (Fig. 20), thereafter the divisions become irregular,three-celled, four-celled, five-celled, and six-celled stageshaving been observed in various instances. Nor is theresult of the final segmentation a hollow vesicle or blas-tula, but a solid mass of cells, termed a morula, is structure is not, however, comparable to the blastulaof the lower forms, but corresponds to a s
The development of the human body; a manual of human embryology . proceed with that regularitywhich marks the segmentation of Amphioxus or an amphi-bian, but while at first it divides into two slightly unequalcells (Fig. 20), thereafter the divisions become irregular,three-celled, four-celled, five-celled, and six-celled stageshaving been observed in various instances. Nor is theresult of the final segmentation a hollow vesicle or blas-tula, but a solid mass of cells, termed a morula, is structure is not, however, comparable to the blastulaof the lower forms, but corresponds to a stage of reptilian * The segmentation of the human ovum has not yet been observed;what follows is based on what occurs in the ovum of the rabbit, mole,and especially of a bat (Van Beneden). 6o THE DEVELOPMENT OF THE HUMAN BODY. development a little later than that shown in Fig. 19,since, as will be shown directly, the cells corresponding tothe blastoderm and the enveloping layer are alreadypresent. There is, then, no blastula stage in the mamma-lian
Size: 1736px × 1439px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1900, booksubjectembryol, bookyear1902
