In amniotes, the cells of the morula are at first closely aggregated, but soon they become arranged into an outer or peripheral layer, the trophoblast, which does not contribute to the formation of the embryo proper, and an inner cell mass, from which the embryo is developed. Fluid collects between the trophoblast and the greater part of the inner cell-mass, and thus the morula is converted into a vesicle, called the blastodermic vesicle. The inner cell mass remains in contact, however, with the trophoblast at one pole of the ovum; this is named the embryonic pole, since it indicates the location where the future embryo will develop.