140 



TEMPERATURE AND EMBRYONIC DEVELOPMENT 



Provide adequate space at a controlled 18°C. environment for 10 finger bowls. Insem- 

 inate eggs of Rana pipiens, and at the 2-cell stage separate them into groups of 25 per 

 finger bowl of 50 cc. of Standard Solution at 18°C. Place two (2) of these finger bowls 

 at the control temperature and four each at the upper limit (29°C. ) and at the lower limit 

 (IOC). At intervals of 6, 24, 36, and 48 hours remove a finger bowl of eggs from each 

 of the extreme temperatures and place it at the control temperature of 18°C. There 

 should be no radical or sudden change in temperature, rather a gradual adjustment within 

 the original medium. Record the stage of development of 50% of the embryos at daily- 

 intervals up to about 12 days (when feeding begins). 



EFFECT OF (VIABLE) TEMPERATURE CHANGE ON SUBSEQUENT 

 DEVELOPMENT STAGE* AND CONDITION OF EMBRYOS 



TIME IN DAYS** 



There is a second method of approaching this problem. The eggs can be left at the ex- 

 treme temperatures from one stage to another, and then returned to the control environ- 

 ment and allowed to develop. The time factor would necessarily be so variable, with 

 three temperatures involved, that this procedure is impractical. 



Development in all cases should be normal, particularly if the temperature shift back to 

 the control temperature is gradual. Note especially the relative stage of development at 

 the termination of the experiment (i. e. , 12 days). 



OBSERVATIONS AND TABULATION OF DATA: 



The normal rates of development at five (viable) temperatures should be recorded 

 and plotted on a separate graph for each different species used. Compare with 

 (Moore) graphs reproduced in this exercise. 



* Most advanced stage of at least 509< of the embryos. 

 *♦ Time in days from time of insemination of the eggs. 



