Oviduct

Normally, these are paired structures, but in birds and some cartilaginous fishes, one or the other side fails to develop (together with the corresponding ovary), and only one functional oviduct can be found.

Instead, the most anterior portion ends in a funnel-shaped structure called the infundibulum, which collects eggs as they are released by the ovary into the body cavity.

In amphibians and lungfishes, the oviduct is a simple ciliated tube, lined with mucus-secreting glands that produce the jelly that surrounds the ovum.

In reptiles, birds, and monotremes, the main part of the oviduct is a muscular tube, capable of considerable distension to transport the large eggs that are produced.

The lower portion of the oviduct, or uterus, has a thicker layer of smooth muscle and contains the glands that secrete the egg shell.

In many placental mammals, the uteri of each side become partially or wholly fused into a single organ, although in marsupials they remain completely separate.