Definition: Abortus, or "abortion vessel" in English, is a term used in medicine to refer to any part of the uterus that contains a fetal organ such as a blastocyst or a placenta. The name "abortion vessel" came about because it was thought that fetuses were always formed by one of the three main methods of embryonic development: fertilization (with sperm and egg) in the womb, implantation (in an amniotic sac) in a uterine cavity, or implantation in the fallopian tube. The exact location where a fetus is implanted was not known until 1603 by the English physician Thomas Malthus. He believed that all fetuses would be born alive if fertilization was allowed to occur naturally and that only a small number of these were likely to survive after the initial stages of development. This belief in abortion vessels led to the practice of using them for abortion in various regions around the world, including India, where it became customary. This period of time is known as the "abortion era" because many women sought legal procedures to abort pregnancies at this time. The act of removing a fetus from its uterus through these so-called "abortion vessels" was called caesarean section and is considered a criminal act in most countries worldwide today.