As the tench is of comparatively uncommon occurrence in unenclosed waters, its place among the indigenous fishes of Great Britain has been denied, and it has been supposed to have been introduced from the Continent; a view which, however, is not supported by any evidence, and is practically disposed of by the fact that fossil remains of the fish are found in the Pleistocene deposits of Great Britain.
Many Gastropoda deposit their eggs, after fertilization, enclosed in capsules; others, as Paludina, are viviparous; others, again, as the Zygobranchia, agree with the Lamellibranch Conchifera (the bivalves) in having simple exits for the ova without glandular walls, and therefore discharge their eggs unenclosed in capsules freely into the sea-water; such unencapsuled eggs are merely enclosed each in its own delicate chorion.
They have remained unenclosed and projecting on the surface of the body, as once were the appendages of the four following somites.
Just before this event, however, the fortifications were once more (1534) rebuilt (bits still remain) and extended so as to take in several new suburbs, including that of St Gervais on the right bank of the Rhone which, till then, seems to have been unenclosed (1511-1527).
The extensive tracts of unenclosed and often unirnprovable land, which still cover a large area in the Principality, especially in the five counties of Cardigan, Radnor, Brecon, Montgomery and Merioneth, support numerous flocks of the small mountain sheep, the flesh of which supplies the highly prized Welsh mutton.