With 1 plate and 16 figures in the text)Annual testicular cycles in the lizards Lacerta sicula and L. muralis appear to be regulated by the interaction between seasonal changes in body temperature and an endogenous rhythmicity in thermal responsiveness. Photoperiodism does not appear to be an important factor; i.e. testicular activity does not appear to be regulated by daylength.Following testicular regression in July, the lizards are refractory to sexual Stimulation by high temperatures (i.e. normal preferred levels) for about five months. High temperatures accelerate gonadal regression and prevent recrudescence during late summer. Reduced temperatures stimulate testicular enlargement and spermatid formation during the autumn; this recrudescence can be blocked by treatment with testosterone. Very low temperatures suppress gonadal activity during mid-winter.Maintenance of lizards at constant high temperatures (33°C) starting in July suppresses testicular recrudescence until December. Also, testicular collapse occurs in lizards transferred to high temperatures after recrudescence has started. The gonads are stimulated by exogenous gonadotropins at 33°C during the fall indicating that high temperatures reduce circulating levels of gonadotropins.The refractoriness to high temperatures is "spontaneously" terminated during midwinter (December) under a wide range of photo-thermal conditions. Low temperatures may accelerate the termination of refractoriness. Thereafter, high temperatures stimulate, and are required for the final development of the testes and accessory sexual structures, Thus, the increase in body temperature following hibernation times the onset of breeding in the spring.Temperature also has a marked influence on appetite and growth, independent of photoperiod. Weight gains are greater at 33" than at 2O"C;At 33" there is a tendency for abdominal fat bodies to enlarge but with little hepatic growth; whereas, the reverse occurs at 20°C.

The somatotropic effects of ovine prolactin and bovine growth hormone (GH) were compared in juveniles of the lizard Lacerta sicula sicula. Both hormones stimulated a marked increase (up to 300%) in food consumption. This effect was associated with a pronounced increase in weight gain which involved some fattening and considerable linear growth: the relative amount of lean growth and fattening were the same with both hormones. GH was slightly more potent on a weight basis, but both were highly effective at a dose of 10 ,&day and some response was evident between 1 and 50 &g/day.Total lipid storage was the same under both hormone treatments but lipid distributions in the body differed, especially with regard to the liver. GH promoted splanchnomegaly and lipid storage in the liver whereas prolactin decreased hepatic growth and lipid content. When the two hormones were given together, there was no synergism or additive effect with respect to total growth and the effects of prola&in on the liver were antagonized by the GH.Recent studies with ovine prolactin in male and female Ikcerta sic&a (Family adult male An&s carolinensis (Family 1,acertidae 1967). Mammalian growth hormone (GH)The prolartin activity of this preparation, based on the pigeon crop bioassay, was reported to be has also been shown to increase growth approximately 1 IU/mg. The prolactin prepararates in lizards-in juveniles of A. tion was of ovine origin (NIH PS-7) and assayed carolinen&+-but the details of its actions at a mean potency of 25 IU/mg. The GH conwere not reported (DiMaggio, 1960). such data, we examined the effects of (2) bovine GH; (3) a combination of prolactin and GH: or (4) 0.01 N NaOH (controls). Durexogenous prolactin and GH in juvenile ing the first 40 da,vs, animals received 1 fig 338