Definition of "chorion"

The allantois fuses with the chorion, forming a small round area, the allentochorion. This region becomes the placenta (Fig. 3).

2002, Rovert E. A. Stewart, Barbara E. Stewart, Female Reproductive Systems, entry in Encyclopedia of Marine Mammals, page 425

In this illustration, some license is taken, since the amnion is shown as still separate from the chorion; this is done to illustrate the process of apposition of the amniotic sac to the chorion and to accentuate the interposition of the yolk sac between the amnion and the chorion.

2006, Ona Marie Faye-Petersen, Debra S. Heller, Vijay V. Joshi, Handbook Of Placental Pathology, page 4

The amnion and chorion begin to develop soon after fertilization and continue to grow until about 28 weeks′ gestation.

2007, Susan Tucker Blackburn, Maternal, Fetal, & Neonatal Physiology: A Clinical Perspective‎, page 106

The chorion has a predominantly lamellar structure, the lamellae being two-dimensional networks of protein fibrils.

1994, Klaus Urich, Comparative Animal Biochemistry‎, page 392

Even closely related species may have chorions differing in thickness. In the silkmoths, for example, the chorion of Bombyx is about 25 μm thick while that of Hyalophora is 55 μm thick.

1998, R. F. Chapman, The Insects: Structure and Function‎, page 326

In addition to facilitating gas exchange and water conservation, the chorion must, in some cases, allow uptake of water or liquid nutrients from the environment.

2008, John L. Capinera, Eggs of Insects, entry in John L. Capinera (editor), Encyclopedia of Entomology, page 1290