scala naturae = Great Chain of Being. Species are fixed and arranged hierarchically.
Often known as ontogeny (developmental biology - the process by which organisms grow and develop) recaptulates phylogeny (a proposal of how organisms are related by their evolutionary history).
Ernst Haeckel - theory that tied evolution with embryology; before they are born, organisms pass through developmental stages that look like adult animals of other species in roughly the same order that these other species split off during evolution.
Stages of Prenatal (Atenatal) Development
1. Germinal Period (from conception to implantation)
Conception is the beginning of the germinal period of prenatal development. This stage occurs during first 2 weeks of development (or 2nd-4th weeks of pregnancy).
Union of sperm and egg cell forms a single cell called a zygote. The zygote moves along the fallopian tube towards the uterus. At the same time, the zygote is rapidly dividing in a process called cleavage.
Once it reaches the uterus, the zygote becomes a blastocyst, and it begins to implant into the wall of the uterus. The germinal period ends when the blastocyst is fully implanted into uterine tissue.
2. Embryonic Period
Lasts from implantation until about 8 weeks from the time of conception (or 10th week of pregnancy). Most important…