Fetus in fetu is a rare variety of parasitic twins, where the developmentally abnormal parasitic twin is completely encapsulated within the torso of the otherwise normally developed host twin.

The Y-chromosome is one of a pair of chromosomes that determine the genetic sex of individuals in mammals, some insects, and some plants. In the nineteenth and twentieth centuries, the development of new microscopic and molecular techniques, including DNA sequencing, enabled scientists to confirm the hypothesis that chromosomes determine the sex of developing organisms.

Telomerase is an enzyme that regulates the lengths of telomeres in the cells of many organisms, and in humans it begins to function int the early stages of embryonic development. Telomeres are repetitive sequences of DNA on the ends of chromosomes that protect chromosomes from sticking to each other or tangling. In 1989, Gregg Morin found that telomerase was present in human cells. In 1996, Woodring Wright and his team examined human

During the twentieth and twenty-first centuries, Robert Paul Lanza studied embryonic stem cells, tissues, and endangered species as chief scientific officer of Advanced Cell Technology, Incorporated in Worcester, Massachusetts. Lanza's team cloned the endangered species of gaur Bos gaurus.

The Southern Gastric-Brooding Frog (Rheobatrachus silus) was an aquatic frog that lived in south-east Australia. In 2002, the International Union for Conservation of Nature Red List declared the frog extinct, although no wild specimens had been

The Spemann-Mangold organizer, also known as the Spemann organizer, is a cluster of cells in the developing embryo of an amphibian that induces development of the central nervous system.

Mesoderm is one of the three germ layers, groups of cells that interact early during the embryonic life of animals and from which organs and tissues form.

Sir John Bertrand Gurdon further developed nuclear transplantation, the technique used to clone organisms and to create stem cells, while working in Britain in the second half of the twentieth century.

The Silent Scream is an anti-abortion film released in 1984 by American Portrait Films, then based in Brunswick, Ohio.

At the turn of the twentieth century, Edmund B. Wilson performed experiments to show where germinal matter was located in molluscs. At Columbia University in New York City, New York, Wilson studied what causes cells to differentiate during development. In 1904 he conducted his experiments on molluscs, and he modified the