A reference handbook of the medical sciences, embracing the entire range of scientific and practical medicine and allied science . e added to the blasto-derm in the region of thegerm-wall. The blastoderm that hasbeen produced by the seg-mentation of the ovum hasbeen called the primaryblastoderm. When, dur-ing the process of gastru-lation, the blastoderm hasbeen differentiated intothree germ-layers, it be-comes the secondary blas-toderm. There are two chief typesof blastoderm: the piscineof elasmobranchs andteleosts, and the saurop-aidan of reptiles, birds,and monotremes. In theformer, the embr
A reference handbook of the medical sciences, embracing the entire range of scientific and practical medicine and allied science . e added to the blasto-derm in the region of thegerm-wall. The blastoderm that hasbeen produced by the seg-mentation of the ovum hasbeen called the primaryblastoderm. When, dur-ing the process of gastru-lation, the blastoderm hasbeen differentiated intothree germ-layers, it be-comes the secondary blas-toderm. There are two chief typesof blastoderm: the piscineof elasmobranchs andteleosts, and the saurop-aidan of reptiles, birds,and monotremes. In theformer, the embryonal areaappears at the posteriormargin of the blastodermand is continuous with afold that on botheroove is forming at the edge sides for some distance•f the blastoderm. (.\fter around the margin of theHert»-ig.) blastoderm (Fig. ) and finally forms the lip of theblastopore. That part of the margin which is notoccupied by the marginal fold forms a zone of over-growth which advances over the yolk with the growthof the blastoderm until the yolk is finally the sauropsidan blastoderm (Fig. ) the. Fig. —Egg of ScylliumCanicula. The lif^hter area isthe blastoderm resting upon theilarker yolk. The medullary marginal fold is transitory, disappearing at an earlystage, after which the whole p(^ri])hiry of tlie blasto-derm consists of a zone of overgrowtli (Fig. 660),which advances over the yolk and finally i^ embryo arises near the center of the blastodermin connection with the primitive streak, which isdescribed with the other structures of the blastodermin another article. (See Area Emhryonalis.) The blastoderm of the Gymnophiona shows somevery interesting features intermediate in structurelietween tlie two main types.
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Keywords: ., bookauthorbuckalbe, bookcentury1900, bookdecade1910, bookyear1913
