158 TEMPERATURE AND EMBRYONIC DEVELOPMENT 



1. Place two finger 'bowlB of medium at each of the five controlled temperatures 

 (listed on preceding page) for 2^+ hours prior to beginning the observations. In- 

 to each place 50 cc- of the appropriate medium for the embryos to be studied. Use 

 Standard Solution or Spring Water for Anura and Urodele Growing Medium for any 

 Urodeles. 



2. Inseminate eggs of Bana plpiens 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 tempera- 

 tures). See that the bowls are covered to reduce evaporation. 



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

 development at l8°C. At frequent intervals, particularly during the first 2k 

 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 2U hour intervals for a total of about 12 days, or until the 

 embryos at the higher temperature level begin to require an external source of 

 food. 



STUDENT RECORD 



