TEMPERATURE AND EMBRYONIC DEVELOPMENT 



llv3 



EFFECT OF (VIABLE) TEMPERATUBE CHANGE ON SUBSEQUENT DEyELOPMENT 

 STAGE*!- AND CONDITION OF EMBEYOS 



TIME IN DAYS** 



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

 extreme 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 develop- 

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



OBSERVATIONS AND TABULATION OF DATA : 



a. 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. 



b. Eggs exposed to extremes of temperature prior to the first cleavage are likely to 

 show numerous abnormalities, and may (Witschi, 1950) even show some imbalance of 

 the sex ratio if carried to the time of sex identification (i.e., metamorphosis). 



c. Subjection of the pre-gastrula embryos to extremes of temperature change is apt 



to interfere with the normal progress of gastrulation and may produce spina-bifida 

 and other manifestations of interference with the "organizer" activity of the 

 dorsal lip of the blastopore. 



* Most advajiced stage of at least 50^ of the embryos. 

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



