Fig. 1 The generation of the archegonium of the fern Macrothelypteris torresiana under light microscopy. (A-B), A primary cell (PC); (C), The central cell (CC) and mononucleated neck canal cell (MNC); (D-E), The young egg cell (EC), the ventral canal cell (VCC) and the neck canal cell (NCC); (F), The stage of maturing egg cell; (G), The separation cavity (SC) between the egg cell and the ventral canal cells (VCC) gradually formed; (H), Complete separation of the egg cell and the ventral canal cells; (I), Fertilization pore (FP) formation; (J), The archegonium in mature egg stage; (K), Jacket cell of the archegonium bend to the base; (L), At the matured egg anaphase, the neck canal cell and the ventral canal cell have completely degenerated. FP, Fertilization pore; SC, Separation cavity.

Fig. 2 Electron microscopic charts of archegonium development and the oogenesis of Macrothelypteris torresiana. (A), The central cell (CC) and the mononucleated neck canal cell (MNC); (B), The amplification of the mononucleated neck canal cell (MNC) and its organelles; (C), Neck canal cell (NCC) and central cell (CC); (D), The 4-5 layer height of the archegonium in the young egg stage; (E), The ventral canal cell (VCC) presenting convex lenticular shape; (F), The ventral canal cell (VCC) and the egg cell (EC) have developed organelles. M, Mitochondria; N, Nucleus; P, Plastid; Ve, Vesicles; Pd, Plasmodesmata.

Fig. 3 Electron microscopic charts of the oogenesis of Macrothelypteris torresiana. (A), Plasmodesmata are connected between ventral canal cell (VCC), the neck canal cell (NCC) and the egg cell (EC); (B), The nuclear of the egg remain unchanged, the nuclear of the ventral canal cell is located in the center; (C), Ventral canal cell degenerated completely and a large number of amorphous substances appeared in the ventral canal cells; (D), The egg cell have deformed nucleus (N) and the egg envelope (EE) begins to accumulate; (E), Under the egg envelope, there are developed mitochondrial and plastids; (F), Circle endoplasmic reticulum (ER) and vesicle containing the osmiophilic materials (Veo) appeared in the egg. M, Mitochondria; N, Nucleus; P, Plastid; Ve, Vesicles; ER, Endoplasmic reticulum; SC, Separation cavity.

Fig. 4 Electron microscopic charts of the oogenesis of Macrothelypteris torresiana. (A), Separation of the pore region from the ventral canal cell (VCC) and a fertilization pore (FP) appears; (B), Arcuate egg; (C), The ventral cancal cell (VCC) and the neck canal cell (NCC) are completely degenerated; (D), Organelles in mature egg cell; (E), A side of egg cell (EC); (F), The separation of the egg from the jacket cell of the archegonium. M, Mitochondria; N, Nucleus; P, Plastid; SC, Separation cavity; FP, Fertilization pore; EE, Egg envelope.

Fig. 5 Potential evolution path of oogenesis of Eupolypods. (A), Eupolypods I, an egg envelope and a fertilization pore (lateral) are formed in the late stage of egg development, the egg nucleus is irregular and produces extensive evaginations; (B), Eupolypods II, an egg envelope and a fertilization pore (lateral) are formed in the late stage of egg development, the egg nucleus is irregular and produces extensive evaginations; (C), Cyatheales, an egg envelope and a fertilization pore (central) are formed in the late stage of egg development, the egg nucleus is irregular and produces extensive evaginations; (D), Gleicheniales, an egg envelope and a fertilization pore (central) are formed in the late stage of egg development, the egg nucleus is regular and produces a few evaginations; (E), Fundamental group of Leptosporangiates, there is no egg envelope and fertilization pore at the later stage of egg development. The egg nucleus is regular and do not produce evaginations. VCC, The ventral canal cell; EC, Egg cell; N, Nucleus; SC, Separation cavity; FP, Fertilization pore; EE, Egg envelope.