Electron microscope examination of thin sections of bullfrog (Rana catesbeiana) ovarian oocytes has shown the presence of mitochondria containing yolk-crystal inclusions in oocytes of all sizes, from 160 to 1500 micro mean diameter. The hexagonally shaped yolk-crystals have major periodicities of 73.8 +/- 10.7 A (n = 100). Several forms of modified mitochondria, observed in the smaller oocytes,...

The effects of a prelay 6/85-strain Mycoplasma gallisepticum (6/85 MG) inoculation alone or in conjunction with subsequent F-strain M. gallisepticum (FMG) inoculations during lay on the internal egg characteristics of commercial egg-laying hens were investigated. In the first 2 treatment groups, birds were sham inoculated or were inoculated with 6/85 MG at 10 wk of age. In a third treatment gro...

I N almost all embryos yolk becomes converted into cytoplasm. It has not previously been possible to describe in any detail the morphological changes involved in this process; indeed, when the yolk drops contained within embryonic cells are examined by light microscopy they seem to remain in much the same condition until they are suddenly used up. For this reason they have frequently been consi...

Yolk sac tumour is germ cell tumour commonly found in children and infants under three years of age in its pure form with a good prognosis. The commonest location for the yolk sac tumour is gonads i.e. testis and gonads. Yolk sac tumour is rarely reported in extra- gonadal locations. Parapharyngeal space is an uncommon site for mature teratoma and very few cases have been reported in adults and...

Recent studies on hormone-mediated maternal effects in birds have highlighted the influence of variable maternal yolk androgen concentration on offspring phenotype, particularly in terms of early development. If genetic differences between laying females regulate variation in yolk hormone concentration, then this physiological maternal effect is an indirect genetic effect which can provide a ba...

Yolk sac tumor is a rare germ cell neoplasm occurring mainly in the gonads. Extragonadal yolk sac tumor is a very rare malignancy; its main distribution is along the midline of the body at three principal sites: mediastinum, central nervous system and retroperitoneum. Most yolk sac tumors are diagnosed between seven months and three years of age. We report a case of primary yolk sac tumor in a ...

Pregnancies with a very large yolk sac are generally always associated with poor outcomes. Herein, we present a case in which a very large yolk sac (mean diameter, 8.1 mm) and a bicornuate uterus were shown on transvaginal sonography in the first trimester, but which resulted in a live birth. To our knowledge, this is the largest yolk sac among all cases accompanying live births which have been...

Electron microscope examination of thin sections of bullfrog (Rana catesbeiana) ovarian oocytes has shown the presence of mitochondria containing yolk-crystal inclusions in oocytes of all sizes, from 160 to 1500 μ mean diameter . The hexagonally shaped yolk-crystals have major periodicities of 73 .8 f 10.7 A (n = 100) . Several forms of modified mitochondria, observed in the smaller oocytes, ma...

Previous experiments have proved that thermodynamically unstable calcium carbonate vaterite can exist for long periods in the yolk sac of a pigeon embryo. The aim of this article was to demonstrate the effect of in vitro mineralization of yolk sac fluid on calcium carbonate by direct precipitation. Experiments were conducted using pigeon yolk sac fluid and using lecithin extracted from pigeon y...

During embryogenesis, organisms with lecithotrophic indirect development usually accumulate large quantities of energetic reserves in the form of yolk that are necessary for larval survival. Since all sponges have lecithotrophic development, yolk formation is an ineludible step of their embryogenesis. Sponge yolk platelets have a wide range of morphological forms, from entirely lipid or protein...