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 IO 

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

 6 and 15 it was between 2.6 and 4.5; between 10 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. Ztschr., 1911, xxxvi., 345; Loeb J., and Cham- 

 berlain, M. M. f Jour. Exper. ZooL, 191 5, xix., 559. 



