In 1938, he discovered that rickettsia could be grown in fertile egg membranes, which led to the development of vaccines to combat Rocky Mountain spotted fever and vaccines for several strains of typhus.
12.
Hertwig, on the basis of examining sea urchins, discovered and explained the zygote fertilization process for the first time correctly as a fusion of egg and spermatozoon ( sperm cell ) penetrating the egg membrane.
13.
Some of these look like early relatives of modern amphibians, most of which need to keep their skins moist and to lay their eggs in water, while others are accepted as early relatives of the amniotes, whose waterproof skin and egg membranes enable them to live and breed far from water.
