Temperature Tolerance and Rates of Development in the Eggs of Amphibia

Although the effect of temperature on the rate of embryonic growth in Amphibia was known before the turn of the last century, it remained for Lillie and Knowlton ('97) to supply the first quantitative data on the subject. They found that as the temperature was increased above the lowest at which eggs of Amnbystoma tigriium or Rana pipiens can develop, the time necessary to reach a given morphological stage becomes progressively less, until a temperature is reached above which normal development does not occur. It was also recognized that the time-temperature curve resembles those "measuring the rapidity of known chemical processes at different temperatures." In view of the work to be presented, it is of interest that they found the temperature tolerance of eggs to be correlated with environmental conditions. The eggs of species breeding early in the year when the water was cold, could tolerate a lower temperature than could those of forms breeding later in the spring. This paper of Lillie and Knowlton was followed by the masterly investigations of Hertwig in 1898, and others such as those of Galloway ('00), King ('03), Chambers ('08), Krogh ('14), Dempster ('33), Atlas ('35), and Knight ('38). The present investigations are concerned with a comparison of the effects of temperature on the embryos of different amphibians. The temperature tolerance and rates of development, over a wide range of temperatures have been determined in four species of frogs. A comparison of developmental rate among four species of salamanders and between two toads has been made. Correlations between temperature tolerance and rates of development on one hand, and breeding habits and geographic distribution on the other, have led to certain conclusions regarding adaptation to environmental temperature