Centrechinoida 557 



In various types of investigations it is desirable to make preliminary 

 tests of each egg-set to be used, in order to determine in advance its 

 behavior with reference to the problem under study. Since eggs can 

 stand for several hours without adversely affecting cleavage, as already 

 noted, the time required for making such tests does not result in 

 deterioration of the material — at least with reference to most fac- 

 tors. 



During the major portion of the season, the capacity of a sample of an 

 egg-set to raise practically 100', normal fertilization membranes indi- 

 cates that it is in prime condition. But this statement does not hold true 

 late in the season, when sets may raise ioo f % normal fertilization mem- 

 branes but nevertheless not cleave properly. Dr. Chambers has observed 

 that some egg-sets obtained late in the season do not have the same con- 

 stancy of size as mid-season eggs; they also require heavier insemination ; 

 and the fertilization membranes lift slowly — in four to five minutes. 

 Preliminary tests are of special value, therefore, toward the end of the 

 season, to separate the egg-sets which are normal from the subnormal 

 ones (Fry, 1936). (See also p. 18.) 



Dr. Ethel B. Harvey stores a large number of Arbacia in laboratory 

 aquaria in early August, when they are still in excellent condition. For 

 some unknown reason their gonads and gametes remain normal until very 

 late in the season, long after those of freshly collected individuals are use- 

 less. 



Just uses Echinarachnius to feed Arbacia, "thus restoring the sea 

 urchins previously in poor condition to a high degree of excellence" 

 (1928). 



Just describes various methods for removing the jelly from the eggs 

 (1928): (1) adding HCL to the seawater; (2) shaking; (3) centri- 

 fuging; and (4) using bolting cloth. Dr. Chambers removes jelly by 

 shaking the eggs in seawater to which isotonic NaCl has been added. 

 A resume of the methods for activating Arbacia eggs artificially, to- 

 gether with a bibliography of the subject, is presented by Morgan ( 1927, 

 Chapter 27). 



Bibliography 



Fry, Henry J. 1936. Studies of the mitotic figure. V. The time schedule of 



mitotic changes in developing Arbacia eggs. Biol. Bull. 70:89. 

 Goldfarb, A. J. 1929. Changes in agglutination of aging germ cells. Ibid. 57:350. 

 Harvey, E. Newton. 1932. Physical and chemical constants of the egg of the 



sea urchin, Arbacia punctulata. Ibid. 62:141. 

 Just, E. E. 1928. Methods for experimental embryology with special reference to 



marine invertebrates. The Collecting Net, Woods Hole, Mass. Vol. 3. 

 Morgan, Thomas Hunt. 1927. Experimental embryology. Columbia University 



Press. 



