11. TEMPERATURE AND EMBRYONIC 



DEVELOPMENT 



PURPOSE: To determine the range of temperature tolerance and the degree of accelera- 

 tion or retardation of development conditioned by the single factor, temperature. 



MATERIALS: 

 Biological: 



Technical: 



Recently fertilized eggs of any amphibian. 



Incubators and refrigerators regulated to within 0. 5 C. at the following 

 . „n^ , „o,- -,nO„ ^, , , . . " 



temperatures: 4. 0°C. , 1 0°C 



20°C. 



The laboratory temperature is 



generally about 23 -25 C. and running tap water ranges from about 



11°C. to 20°C. 



METHOD: 



Precautions : 



1. The incubators and refrigerators should be checked daily, and the exact 

 temperature recorded. 



2. A reserve supply of culture medium should be kept at the various temperatures, 

 so that changes can be made without altering the temperature. 



3. The number of eggs and embryos per finger bowl of known volume of medium 

 should be the same for all observations. The usual ratio is 25 eggs per 50 

 cc. of medium. 



Controls : The control series may consist of eggs kept at the (fluctuating) laboratory 

 temperatures. This represents the normal, or average condition for most of the 

 experiments in this course. However, there is a breeding temperature which 

 must be optimum for each of the various available amphibian eggs. The ideal 

 control temperature would therefore be this optimal breeding temperature. 

 Moore (1942) gives these data in the following tabular form, for five species of 

 Rana. For various Urodeles, consult other tables on the following pages: 



The relation between breeding habits, geographic distribution, and certain 

 embryological characters in frogs of the genus Rana. 



Moore 1942: Biol. Symp. 6:189. 



Procedure : There are two distinct investigations included in this exercise: 



1. Determination of the developmental rate at five different controlled tempera- 

 ture levels. 



2. Effect on development of temporary exposure to a radically different tem- 

 perature during certain critical stages of development. 



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