In growing individuals, narrow zones of new epidermis form on the
laminae in spring. Nearly all the growing individuals collected in May
of 1954 and 1955 had zones of new epidermis on the shell but those
collected in April did not. Activity in the first week or two after
spring emergence is sporadic and regular feeding may not begin until
early May. Once begun, growth is more or less continuous as long as
environmental conditions permit foraging. The formation of minor
growth-rings and adjacent growth-zones in autumn, provides evidence
that growth commonly continues up to the time of hibernation. The
number of growing days per year varies, of course, with the
favorableness of environmental conditions. The length of time (162
days) given by Fitch (1956b:438) as the average annual period of
activity for _T. ornata_ is a good estimate of the number of growing
days per season.