General principles of zoology . thisballast increases in relation to the protoplasm, so muchthe more slowly does the cleavage process there comes a point where the resistance of theyolk becomes so great that the protoplasm is no longerable to completely carry out the work; then only theprotoplasmic part of the egg is divided, that which is richin yolk remaining an undivided mass. In this case, onespeaks of a partial cleavage in comparison with the ordi-nary and more primitive mode, the total cleavage; further,the eggs which show a partial cleavage are called mcro-blastic, becau
General principles of zoology . thisballast increases in relation to the protoplasm, so muchthe more slowly does the cleavage process there comes a point where the resistance of theyolk becomes so great that the protoplasm is no longerable to completely carry out the work; then only theprotoplasmic part of the egg is divided, that which is richin yolk remaining an undivided mass. In this case, onespeaks of a partial cleavage in comparison with the ordi-nary and more primitive mode, the total cleavage; further,the eggs which show a partial cleavage are called mcro-blastic, because only the segmented part of the egg isdirectly employed in the formation of the embryo or bud(/?A«<TTOS), while the undivided main mass serves merely asfood-material in the course of growth. Eggs with totalcleavage, on the contrary, are called holoblastic. Distribution of the Yolk.—As to the second point,the arrangement of the yolk : this is connected with theposition of the nucleus; either the egg-nucleus maintains Pd. - n
Size: 1586px × 1576px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1890, booksubjectzoology, bookyear1896
