Leishmania spp. survive in the mammalian host by using the ability of host macrophages to engulf invading organisms. Once engulfed, the amastigote divides by binary fission, and is eventually released when the macrophage bursts. Other macrophages engulf these amastigotes, and the cycle repeats.
This photo shows a macrophage with two small amastigotes (arrow) within. The amastigote at the 1 o'clock position shows typical morphology: a spherical shape; a large nucleus; and a small, peripheral, darkly staining body that is the characteristic internal flagellum of the amastigote stage.