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 It is suggested that terms linked with outdated concepts are not always appropriate for, and unless defined with care may limit, our appreciation of the significance of subsequent observation and experiment.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.