Redistribution Of Contents Research Articles

Nests, eggs, and embryonic development of Carettochelys insculpta (Chelonia: Carettochelidae) from Northern Australia

Ten Curettochelys insculptu nests from the Daly River, in the Northern Territory of Australia, are described. Eggs were in sand banks beside the river and were laid during August and September, in the dry season. Mean clutch size was 12.7±3.3 eggs (SD). Eggs are hard‐shelled and spherical (mean egg diameter 38.7 k0.13 mm) and weigh 33.7±3.5 g. Embryonic development rate varies as a function of incubation temperature. Using as an endpoint the stage at which residual yolk is internalized, incubation times are approximately 53 days (at 32° C), 69 days (30° C) and 101 days (28° C). Embryonic metabolic rate increases exponentially during early development and is highest when the residual yolk is internalized. Hatching is delayed for a considerable period after yolk internalization (224±8.6 days at 30° C and 32° C). During the period between yolk internalization and hatching (the ‘hatching delay’) metabolic rate decreases precipitously, embryonic growth ceases and 0.04‐0.05 g of yolk (at 28° C to 32° C) plus an unmeasured amount of body fat are used for maintenance each day. Hatching can be stimulated by reducing oxygen availability, either through submerging eggs in water or perfusing them with nitrogen. In the field hatching is probably stimulated by early wet season rains and/or rises in water level. Total egg weight losses during incubation varied between 1% and 11% of the original weight, but no significant relationship between weight loss and hatchling size could be demonstrated. Hatchling size is largely determined by egg size and development rate. Formulae for predicting various hatchling dimensions from each other and from egg size are presented. The redistribution of egg contents that occurs during development and the spreading field of shell opacity that accompanies development are both described. The proportion of albumen and yolk in Curettochelys insculpta eggs is similar to that in marine turtle eggs, which is consistent with a minimum amount of water‐laden albumen being necessary for yolk rotation to occur after laying (to position the embryo on the upper surface of the egg). Curettochelys insculptu has environmental sex determination. Embryos incubated at 28° C and 30° C become males whereas those incubated at 32° C become females. Females have smaller body sizes and a greater mass of residual yolk than males from eggs of the same size, but these differences appear to be consequences of varying development rates rather than being linked in any causal fashion with sex.

Greenstones related to rifting and ocean basin opening in the Jofjället area, central Swedish Caledonides

Abstract Two greenstone formations in the Jofjället area, central Swedish Caledonides, have been analysed for major and trace elements in order to establish their petrology and tectonic environment of origin. The formations — the Ruffe Greenstone and the Brackfjället Greenstone — are situated in the uppermost part of the Seve-Köli Nappe Complex. The enrichment in volatiles, depletion in SiO2, redistribution of CaO and alkali contents are certainly caused by post-eruptive alteration processes. The Ruffe Greenstone is a tholeiite of a transition type between ocean-floor and within-plate basalt, while the Brackfjället Greenstone is an alkaline basalt showing a clear within-plate basalt affinity. The basalts are possibly formed during the later stages of rifting and ocean basin opening in a near-continental environment. The basalts can probably be correlated with the Støren greenstone in Norway.

Formation of Giant Cells in Vivo

In vivo, the development of multinucleate giant cells in granulomas always proceeds in accordance with a given mode (simultaneous phagocytosis - fusion - unordered multinucleate giant cells - ordered multinucleate giant cells). This mode is both quantitatively and qualitatively modifiable, showing a dependance on the quantity, shape, size, and digestibility of the phagocytic material: on uncoated coverslips implanted i.p. in rats, only a few small syncytia develop, bit by bit, on coverslips coated with phagocytotic material, on the other hand, numerous very large, always initially unordered, multinucleate syncytia showing simultaneous aggregation around large phagocytic objects are seen. These can develop into ordered giant cells of the Langhans type, by re-distribution of the cytoplasmic contents, but only when most of the phagocytosed material has been digested. Actively phagocytosing mononuclear macrophages, which coalesce or have already fused to form syncytia frequently develop various types of junctions that probably have the same function in granulomas as in epithelia. Pentalaminar structures in multinucleate giant cells are frequently observed in close conjunction with residual phagocytic material and obviously represent outer cell-membranes that have coalesced during fusion and been incorporated into the cytoplasm. The clear zones surrounding such areas probably represent an element of the cytoskeleton.

Gastric motility and emptying in normal and post-vagotomy subjects.

The effects of proximal gastric vagotomy (PGV) and vagotomy with pyloroplasty (V and P) on gastric motility were studied using a solid meal labelled with a radiopharmaceutical agent. In having on-line computer facilities it was possible not only to record the rate of emptying but also to analyse the relative roles of the fundus and the antrum within the overall framework of gastric emptying. In normal subjects the fundus filled and then emptied in an almost linear pattern. The antrum, however, did not completely fill until well after the meal was eaten and thereafter appeared to maintain a constant volume during the study. The redistribution of contents between fundus and antrum was reflected in the total stomach emptying curve as a delay, or lag phase before gastric emptying commenced. After both types of vagotomy fundic filling was delayed, representing a slower eating time, which was presumably due to early satiety. Antral filling and volume was disturbed only after V and P, which was also reflected by a loss of the lag phase seen on the total stomach curve. PGV retained antral function but there was significant delay in the redistribution of contents between fundus and antrum, though this did not have clinical significance. The rate of emptying was unaffected by either operation. It was concluded PGV did maintain antral function and a more normal pattern of emptying compared with V and P. After V and P the changes in antral function were considerable and these changes are probably associated with some of the complications resulting from this operation.

Spatial and Temporal Changes in Early Amphibian Development

Following fertilization in Xenopus eggs, the dorsal-ventral asymmetry of the egg is established and a rapid cell cycle is begun. In the mid to late blastula period this initial asymmetry is translated into differentiation of the dorsal mesoderm initiated by the vegetal dorsalizing center; as suggested by experiments of Nieuwkoop. About this time the cell cycle undergoes a modification coincident with several events including the onset of cell motility. We report here on experiments describing how the dorsal-ventral asymmetry is produced in the early period. In particular we discuss the role of the sperm, its associated aster, the cortex, and redistribution of cytoplasmic contents. This analysis furthers our understanding of UV effects on dorsalization and the mechanism of twinning. We report also on evidence for a cytoplasmic clock regulating the cycle of DNA synthesis and cytokinesis in early cleavage, as well as on further experiments on the mechanism of cell cycle changes in the midblastula period.