. The elasmobranch fishes. Chondrichthyes. 308 THE ELASMOBRANCH FISHES processes from the yolk sac of the embryo form close attachment to the uterine wall. Through this attachment nutriment may be secured by the embryo. The relation of the uterine wall to the embryo in Mustelus antarcticus (fig. 268) shows still another widely different relationship. In this form, according to T. J. Parker (1882), the uterus, by the ingrowth of its lining, becomes yi^ '• A ^J^ %. Fig. 269. Development of the butterfly ray, PteropJatea micritra. (From Alcock.) A. The embryo in the uterus. B. A tip of a single v
. The elasmobranch fishes. Chondrichthyes. 308 THE ELASMOBRANCH FISHES processes from the yolk sac of the embryo form close attachment to the uterine wall. Through this attachment nutriment may be secured by the embryo. The relation of the uterine wall to the embryo in Mustelus antarcticus (fig. 268) shows still another widely different relationship. In this form, according to T. J. Parker (1882), the uterus, by the ingrowth of its lining, becomes yi^ '• A ^J^ %. Fig. 269. Development of the butterfly ray, PteropJatea micritra. (From Alcock.) A. The embryo in the uterus. B. A tip of a single villus highly magnified. divided up into as many rooms as there are embryos within the uterus. The uterine wall is composed of an outer peritoneal lining (p.), a second or thin muscular layer (m.), and a third or inner mucous lining (mu.). It is the last- named layer that grows out to form the partitions separating the uterus into rooms. These rooms are filled with fluid in which the embryos lie and by which they are protected. In this type of Elasmobranch we see a device for protecting the developing young which, in a way, is like that in higher animals. In this form, however, the protective sac is produced by the maternal tissue, while in higher forms it is formed by the embryo. In Pteroplatea micrura the villi or papillae on the uterine wall of the mother may be numerous and those which are over the spiracle of the embryo become long and strap-shaped (fig. 269a) . In an embryo that is far advanced the yolk. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Daniel, J. Frank (John Franklin), 1873-1942. Berkeley,Calif. , University of California press
Size: 1255px × 1990px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookpublisherberkeleycalifuniversityofcaliforn
