TEMPERATURE AND EMBRYONIC DEVELOPMENT 



139 



2. Subjection of pre-gastrula stage to radical temperatures: The forces involved in 

 gastrular movements are no doubt at work prior to any indication of these morpho- 

 genetic movements. It is necessary, therefore, in this study to secure eggs (Rana 

 pipiens) at stage #8 or #9 and place these eggs at the supra-maximal and subminimal 

 temperatures, as previously determined, to see whether gastrulation is subject to 

 temperature interference. 



In a manner similar to (1) on the preceding page, prepare 25 eggs per finger bowl of 50 

 cc. Standard Solution and leave them at the controlled room (18°C. ) temperature until 

 they reach stage #8 or #9. In the meantime, provide abundant Standard Solution at 4°C. 

 and at 33 C. , into which the eggs can be transferred for intervals of 1 , 2, 6, and 24 

 hours. Record the effect on gastrulation and subsequent development in the following 

 table. 



PRE-GASTRULATION RADICAL TEMPERATURE TREATMENT 



Effect of temperature change on subsequent rate of development: It has been suggested 

 (Buchanan, 1940; Ryan, 1941) that when eggs or embryos are subjected to low (or 

 high) temperatures, within the viable range, and then returned to the control (normal) 

 temperature, that the effect on the rate of development is such that temporary cold 

 retardation {for instance) causes subsequent acceleration so that the experimentals 

 may even pass the controls. To test this concept, the following procedure is suggested. 



* Most advanced stage of at least 50% of the embryos. 



