136 



TEMPERATURE AND EMBRYONIC DEVELOPMENT 



RATES OF DEVELOPMENT AND TEMPERATURE 



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

 ular 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 simul- 

 taneously. This is possible because within certain limits, acceleration and retardation 

 affect merely the rate of development. 



DEVELOPMENTAL RATE OF RANA AT 19.8°C.* 



1. Place two finger bowls of medium at each of the five controlled temperatures (listed 

 on preceding page) for 24 hours prior to beginning the observations. Into each place 

 50 cc. of the appropriate medium for the embryos to be studied. Use Standard Solu- 

 tion or Spring Water for Anura and Urodele Growing Medium for any Urodeles. 



2. Inseminate eggs of Rana pipiens at laboratory temperatures (or, provide yourself 

 with abundant eggs of any other species in pre-cleavage stage, if possible). Await 

 the first cleavage (2^ hours) and then separate the eggs from the bottom of the finger 

 bowl (by means of a clean section lifter) and allow the jelly to swell further. After 

 about 10-15 minutes, cut the egg mass into groups of 5-10 eggs and place exactly 25 

 eggs in each of the 10 finger bowls (2 each at 5 temperatures). See that the bowls are 

 covered to reduce evaporation. 



3. Consult the Shumway Table of Normal Stages for Rana pipiens, which is based on de- 

 velopment at 18°C. At frequent intervals, particularly during the first 24 hours, 

 examine eggs from each of the temperatures and determine the stage of development. 

 Check the temperature of the medium, and record the stage of the group as the most 

 advanced stage achieved by at least 50% of the eggs. It would be well also to note 

 the extremes in development. The record should thereafter be taken at exactly 24 

 hour intervals for a total of about 12 days, or until the embryos at the higher tem- 

 perature level begin to require an external source of food. 



* Modified from Moore '39, '40, '42, '49. Zero point is first cleavage or two cell stage. 



