Columella regarded the gains from the births as a sufficient motive for encouraging these unions, and thought that mothers should be rewarded for their fecundity; Varro, too, seems to have taken this view.
Viability, by which are meant fecundity, longevity and vigour, was low in average.
Such is their fecundity that it has been asserted that one female (probably of P. vestimenti) may in eight weeks produce five thousand descendants.
In the British Isles the 1 The name of the fishes of the genus Cyprinus is derived from the island of Cyprus, the ancient sanctuary of Venus; this name is supposed to have arisen from observations of the fecundity and vivacity of carp during the spawning period.
That chinchillas have not under such circumstances become rare, if not extinct, is owing to their extraordinary fecundity, the female usually producing five or six young twice a year.