Development of the cloacal bursa in the domestic fowl. II. A quantitative and fine structural analysis of the follicular cortex and medulla.

The estimated volumes of the follicular medulla (x) and cortex (y) from 14-day-old embryos till 28-day-old White Leghorn chicks were associated through the allometric formula y = bxk or log y = log b + k log x. Two successive allometric growth stages (I and II) are discernable, being hatching the transition region between them. The volumetric growth of the cortex is 2.49 times greater than that of the medulla in stage I, whereas cortex and medulla grow isometrically in stage II. The curve fitting procedure analysis of the absolute cortical and medullary growth confirmed these results. The fine structure of the cell types in the follicular medulla revealed that: a) in the allometric stage I pre-existing, bud precursor (Pr) cells appear to give rise to basal (Ba) and medullary epithelial (ME) cells, in both cases showing lucent and dark varieties. A medullary cytoreticulum is established at the onset of this stage. b) The marked lymphocyte proliferation during stage II occurs among the thin and short cytoplasmic processes of BA cells. These processes extend towards the centre of the medulla and also show many lateral interdigitating processes. During this same stage, the cytoplasmic processes of ME cells elongate and become thinner promoting a widening of the cytoreticulum interstices. The fine structural analysis of the cortical cytoarchitectural arrangement showed that: a) before the onset of stage I (14-day-old embryos) the cortex consists mainly of typical fibroblasts (F) and a few blastic (Pr?) cells. Later in this stage I, a poorly defined cortical framework is made up of typical fibroblasts, few cortical branching (CB) cells of the epithelial variety (which seem to be derived from Pr cells) and CB cells of the fibroblast-like variety. These cells are interspersed with mature and immature lymphocytes. b) Allometric stage II of the cortex is characterized by the presence of very thin and long cytoplasmic processes from CB cells of both epithelial and fibroblast-like varieties. The arrangement of CB cell profiles, visualized in electron micrographic montages, is remarkably similar to that of the ME cells profiles which are known to form a cytoreticulum. We thus propose that the mature follicular cortex is endowed with a cellular framework forming wide interstices in which packed mature lymphoid cells are lodged.

[Ultrastructural study of the germinal cells of ovary of Penaeus paulensis (author's transl)]. / Observations ultrastructurales sur la maturation des cellules germinales de l'ovaire de Penaeus paulensis.

The ultrastructural study of the germinal cells of Penaeus paulensis was carried out on the immature (stage I), in maturation (stage II) and mature ovary (stage III). The stage I is characterized by numerous peripheral nucleolar systems which are formed by a fibrillar central portion entoured by a fibrillogranular nucleolonema. There are no yolk granules in the cytoplasm. The stage II is characterized by the onset of the vitellogenesis and a close morphological relationship exists between the endoplasmic reticulum and the systhesis and deposition of yolk. The stage III is recognized by the presence of the "peripheral bodies" in the peripheral cytoplasm of the germ cells. These structures are separated from the adjacent cytoplasm by the cell membrane and possibly represent an accumulation of extracellular material comparable to the zona pellucida.