. The embryology and metamorphosis of the Macroura. Crustacea; Embryology -- Crustacea. MEMOIRS OF THE NATIONAL ACADKMY K SCIENCES. 457 is differentiated from a distinct epithelial cell, the nucleus of the cell becoming or germinal vesicle of the egg. Some of the epithelial cells enwrap I he developing ovum and form the follicle, or pocket in which it is lodged. The chorion or inner egg membrane is the. direct secretion product of the follicnlar cells. (7) -In Homarus and Palinurus the character f the germinal epithelium is somewhat different from that of Alpheus. The outline of in
. The embryology and metamorphosis of the Macroura. Crustacea; Embryology -- Crustacea. MEMOIRS OF THE NATIONAL ACADKMY K SCIENCES. 457 is differentiated from a distinct epithelial cell, the nucleus of the cell becoming or germinal vesicle of the egg. Some of the epithelial cells enwrap I he developing ovum and form the follicle, or pocket in which it is lodged. The chorion or inner egg membrane is the. direct secretion product of the follicnlar cells. (7) -In Homarus and Palinurus the character f the germinal epithelium is somewhat different from that of Alpheus. The outline of individual cells is obscured and the germinal epithelium extends inward from the wall, in the form of radial sheets or folds, between which are reentrant blood vessels. There are a number of gerniogenal areas corresponding to the folds in which the ova originate. During growth the eggs gradually pass from the center toward the, periphery. In the germogeu the cell outlines are obscured.* (8) The yolk arises within the cell protoplasm, and in Ilomarns degenerating nuclei occur in the ovarian stronui, and it is probable that a certain number of nuclei degenerate and enter into the food yolk of the egg. In the lobster also some of the follicle cells develop into gland-like struc- tures which the mature ovary. They appear to have a direct relation to the growing- eggs, but their true significance has not yet been ascertained. In about two weeks after the eggs have been extruded these structures have almost wholly disappeared. (9) 1 have observed a single polar body in a section of the egg of Stenopus, in which the male and female pronuclei were present, and two polar bodies in the ripe unextrnded egg of the lob- ster. In lobster's eggs also which failed of extrusion at the proper time, and which eventually degenerate in the ovary, I find that the nucleus is at the surface. It has the appearance of a female pronncletis. It is thus probable that the polar bodies are often,
Size: 1559px × 1602px
Photo credit: © Paul Fearn / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookauthor, bookcentury1800, bookdecade1890, booksubjectcrustacea
