The Influence of Environment 293 



The time required for the eggs to reach definite 

 stages was measured for different temperatures and 

 it was found that the temperature coefficient Q I0 

 between 2.5 and 6° was equal to 10 or more; between 

 6° and 15 it was between 2.6 and 4.5; between io° and 

 20 it was 2.9 to 3.3, and between 20 and 24° it was 

 between 1.4 and 2.0. To anybody who has worked 

 on this problem it is obvious that no exact figures 

 can be obtained in this way, since the point when 

 a certain stage of development is reached is not 

 so sharply defined as to exclude a certain latitude of 

 arbitrariness. The writer found that very exact 

 figures can be obtained on the influence of temperature 

 upon development of the sea-urchin egg by measuring 

 the time from insemination to the first cell division. 

 Such experiments were carried out in a cold-water form 

 Strongylocentrotus purpuratus and a form living in 

 warmer water, Arbacia. 1 The figures on Arbacia 

 have been verified by different observers in different 

 years. 



1 Loeb, J., Arch. f. d. ges. Physiol., 1908, cxxiv., 411; Loeb J., and 

 Wasteneys, H., Biochem. Zlschr., 1911, xxxvi., 345; Loeb J., and Cham- 

 berlain, M. M., Jour. Exper. Zool.,1915, xix., 559. 



