[Changes in the thermal resistance of tadpole muscle tissue in the common frog in the thermal selection of ova].

Mature ova of frogs have been subjected to doses thermal effects causing death or injury of 5, 50 and 95% of ova. With the increase of intensity of thermal selection all the ova undergo complex internal changes, abruptly shift the ratios of muscle tissue heat resistance values of larvae developed from the ova selected by heating, cause the disappearance of low resistant variants and the appearance of a number of highly resistant variants absent from the control series. The pattern of changes of the heat resistance allows an assumption that these may be due to the existence of at least two groups of ova which response quite differently to the thermal effect. Hence, during an intensive thermal selection of ova, two processes are under way going in parallel: the first, the elimination of low-resistant ova and, consequently, of individuals with low tissue resistance, and the second, a reactive change in ova due to which the larvae with high tissue resistance appear.