Apart from the initial minor damage, the maternal capillaries are not harmed by the penetrating chorionic villi; instead, the capillaries form labyrinthine networks between the villi. Each capillary network becomes surrounded by (1). The (1) is a fused mass of chorionic cells originating from the bases of the villi; the cells lose their internal walls and form a (2) (see Figs. 39 and 40). The (1) is particularly rich in mitochondria and is responsible for (3) nutrition.