. The Biological bulletin. Biology; Zoology; Marine biology. THE POLE DISC OF CHRYSOMELID EGGS. 183. A series of divisions now ensues until a number of bodies, like chromosomes in appearance, is produced in a single space (Fig. 4, c). After about four or five divisions have taken place, they begin to lose their affinity for the basic stain and also their regu- larity of outline (Fig. 4, d), and in the next stage (Fig. 4, e) they are seen to have fragmented into nu- merous irregular bodies that stain with the acid dye. Still later (Fig. 4, /") the space is practically filled with a finely
. The Biological bulletin. Biology; Zoology; Marine biology. THE POLE DISC OF CHRYSOMELID EGGS. 183. A series of divisions now ensues until a number of bodies, like chromosomes in appearance, is produced in a single space (Fig. 4, c). After about four or five divisions have taken place, they begin to lose their affinity for the basic stain and also their regu- larity of outline (Fig. 4, d), and in the next stage (Fig. 4, e) they are seen to have fragmented into nu- merous irregular bodies that stain with the acid dye. Still later (Fig. 4, /") the space is practically filled with a finely granular acid staining yolk mass. The process of yolk formation, therefore, consists in the transfor- mation of the basic staining granules of the food stream into an acid stain- ing yolk which fills the meshes of the cytoplasmic reticulum of the mature egg. In this transforma- tion the cytoplasm as well as the nucleus is undoubtedly involved. The yolk is first laid down in the center of the egg, but as the granules spread outward as well as inward from the nutritive stream it is not long before yolk is found on either side of the food stream. The pole disc does not appear until the egg is nearly mature, and a study of successive stages shows that it is composed of granules of the food stream that have accumulated at the pos- terior end of the egg (Fig. 5). These granules are much larger than those of the Keimhaut (the peripheral layer of cyto- plasm surrounding the yolk in the mature egg) and stain in- tensely with the basic stain. This staining reaction might sug- gest that the granules are of nuclear origin; but while the nucleus at this time is far from inactive, with an interchange of materials between it and the cytoplasm probably taking place, I have never been able to observe an actual emigration of granules from the nucleus into the cytoplasm. Union of the germ nuclei in fertilization and the early cleav- Fig. 3. Section of the cytoplasm of ilie growing ovocyte in the
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