TEMPERATURE AND EMBRYONIC DEVELOPMENT 



FUEPOSE: To determine the range of temperature tolerance and the degree of acceleration- 

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



MATERIALS : 



Biological : Becently fertilized eggs of any amphihian. 



Technical : Incubators and refrigerators regulated to within 0.5°C. at the following 

 temperatures: U.O°C., 10°C., 20°C. The laboratory temperature is gener- 

 ally about 25°-25°C. and running tap water ranges from about U°C. to 20'-'C. 



METHOD : 



Precautions : 



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

 ture recorded. 



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

 30 that changes can be made without altering the temperature. 



5 . 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 inay consist of eggs kept at the (fluctuating) laboratory 

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

 periments in this course. However, there is a breeding temperature which must be 

 optimum for each of the various available amphibian eggs. The ideal control temper- 

 ature would therefore be this optimal breeding temperature. Moore (19'*-2) gives 

 these data in the following tabular form, for five species of fana. For various 

 Urodeles, consult other tables on the following pages. 



The relation between breeding habits, geographic distribution, and certain 

 embryologi cal characters in frogs of the genus Sana. 



Moore I9I+2 : Biol. Symp. 6:189. 



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



1. Determination of the developmental rate at five different controlled temperature 

 levels . 



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

 during certain critical stages of development. 



RATES OF DEVELOPMENT AND TEMPERATURE 



Data from these observations has practical value in that eggs inseminated at any par- 

 ticular time can be apportioned to the various temperatures at which the development is 

 known to be normal, and embryos of various stages will thereafter be available simultane- 

 ously. This is possible because within certain limits, acceleration «m.d retardation af- 

 fect merely the rate of development. 



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