The cock has no penis but a small opening near the vent through which sperms are emitted. Cock has testes within the body.

The hen has elongated oviduct for formation of an egg. Fertilization occurs internally.

During mating the cloaca of the hen and the vent of the cock fit into each other and then semen is poured into the cloaca ,then sucked to the oviducts.

The Reproductive System of a Hen

The reproductive system has the following parts;
i). Ovary
ii). Funnel(infundibulum).
iii). Magnum
iv). Ishtumus
V). Uterus/Shell gland
vii) Vaginal
viii). Cloaca

Ovary

Hen has two ovaries but one functional. Ova is formed in ovaries.
About 3500-4000 ova present inside ovary held by follicle. Mature ovum released via rapture of follicle. It moves into oviduct received by the funnel.

Funnel(infundibulum)
Fertilization occurs here. Chalazae also added to yolk.
It also collects the ovum and stores the sperm. Time here is 15 minutes and it is 11.6cm long.

Magnum
Thick albumen is added and stays for 3hrs. its 33cm long.

Isthmus
Its 10.6cm long, Shell membranes added and determines shape of egg.
Water, mineral salts and vitamins added and takes 15 minutes.

Uterus(shell gland)
Calcium deposits i.e.shell added around the egg. Pigments added.
Addition of albumin finished and stays here for 18-22hours.

Vagina
Short, 6.9cm long and for temporal storage of egg before laying

Cloaca
Egg moves out of cloaca through the vent and the cloaca extents out to prevent the egg from breaking.
NB;
Egg formation not depended on fertilization. Egg formation takes 24-26hours.
The components of egg are obtained from body reserves of the hens body.