The terminology of early development: history, concepts, and current usage.

The meaning of some terms used in describing the development of embryos is discussed in the light of their historical origin and current usage. Attention is focused on the terminology associated with the early development of animals, particularly that concerned with gastrulation and germ layer theory. It is suggested that terms linked with outdated concepts are not always appropriate for, and unless defined with care may limit, our appreciation of the significance of subsequent observation and experiment.

The development of Caretta caretta, at 25-34°C, in artificial nests.

Scanning electron microscopy has been used to enhance the description of a single species, Caretta caretta (the loggerhead turtle), staged according to Miller's system for the development of marine turtles. Incubation over a temperature range of 25°-34°C confirms previous observations that, under artificial conditions and at a constant incubation temperature, normal development is confined to a limited temperature range. Premature pipping is a feature of incubation at the lower end of this range; abnormal development, generated during the first third of the incubation period, occurs just above the normal range.

Mitochondrial number, cytochrome oxidase and succinic dehydrogenase activity in Xenopus laevis oocytes.

An estimate has been made of the numbers of mitochondria in the mitochondrial cloud (Balbiani body) of Xenopus laevis oocytes ranging in size from 50 to 250 micrometers. The mitochondrial number is expressed in terms of a 'standard' organelle measuring 2 micrometers in length and 0.2 micrometer in diameter and is derived by measurements on electron micrographs of sections through the cloud.

The culture of tissue from the ovary of the goldfish Carassius auratus.

Small pieces of ovarian tissue derived from immature goldfish have been maintained in culture periods of up to three months. The progress of the culture was monitored by light and electron microscopy and showed that although degenerative changes occurred in the large oocytes the small oocytes and oogonia survived for the duration of the culture. Quantitative studies indicate that both oogonia and small oocytes increase in number during the first three weeks of culture and observations from experiments using 3H-thymidine support the idea that a limited proliferation can occur using the relatively simple technique described.

Effect of X-rays on Xenopus tadpoles.

Irradiation of Xenopus tadpoles may cause precocious metamorphosis related to deprivation of food caused by gut damage. This makes the interpretation of the effects of X-rays on individual organs systems, such as the gonads, difficult.

The effects of DNA administration on the growth of X-irradiated Xenopus tadpoles.

An easy method for the harmless measurement of the length of tadpoles is described. The results indicate that tadpoles exposed to 3,000 r showed increase in length 20 days following irradiation. The animals exposed to the same or other X-ray doses and administered high molecular homologous and heterologous DNA showed a better rate of growth than the animals exposed to a dose of 3,000 r and not given DNA.

Regeneration of the tail of X-irradiated Xenopus tadpoles.

The effects of X-rays on the regeneration of the tail of Xenopus laevis tadpoles have been studied. Larvae of stage 52 were exposed in groups to irradiation either of the head or the body region with doses of 3,000 and 4,000 r. In both cases, the animals have regenerated the lost parts of their tails.

Effects of X-rays on the spermaries and ovaries of Xenopus tadpoles.

The results show that irradiation affects both the size of the gonads and the number of germ cells they contain. At stage 64, gonads from irradiated animals were smaller than those from unirradiated ones. The reduced length and thickness of gonads of the test animals were probably due to cell killing.

The structure of the mitochondrial cloud of Xenopus laevis oocytes.

The ultrastructure of the mitochondrial cloud (Balbiani body) of the pre-vitellogenic oocytes of Xenopus laevis has been examined using transmission and stereoscan electron microscopy. Examination of conventional thin sections confirm previous observations which suggest that the cloud consists essentially of many thousands mitochondria and numerous small vesicles; larger clouds, in oocytes greater than 200 mum in diameter, contain relatively more vesicles. Using a standard electron microscope at 100 kV very long and coursing arrays of mitochondrial profiles can be detected.