I04 THE AMERICAN ARBACIA 



Cold, Heilbrunn, 1920 b. 



Ether, Heilbrunn, 1920 b. See E. B. Wilson, 1901b for Lytechinus. 



Hydrostatic pressure, Marsland, 1938, 1950, 1951 for A. punctulata ; 



1939 for A. lixula. 

 Micromanipulation, Chambers, 19 19, 1938 c, 1951. 

 Oxygen-lack, Mathews, 1907; E. B. Harvey, 1927 for other species; 



1930 for A. punctulata. 

 Podophyllin, etc., Cornman and Cornman, 1951. 

 Quinine, Mathews, 1907. 

 Urethane, Painter, 19 18; E. B. H., unpub. 



j. Isolation of Mitotic Apparatus 



An important method has been recently devised by Mazia for isolating 

 the mitotic apparatus from the rest of cell and has been applied to 

 Arbacia punctulata (Mazia and Dan, 1952; Dan, Ito, and Mazia, 1952). 

 This technique, the details of which are given in their papers, allows 

 a much better understanding of the structure, function, and chemistry 

 of different parts of the mitotic figure. 



k. Elongation at Cleavage 



Elongation of the Arbacia egg at the time of cleavage is easily observed 

 in the living tgg, as seen in the photographs. Studies have been made 

 on the elongation especially by Churney (1936, 1940). He found that 

 with the fertilization membrane present, the egg elongates from 74 to 

 82.5 [X, an elongation of 1 1.5% (at 22.2-26.0 °C.) ; without the fertih- 

 zation membrane it elongates from 74 to 103.2 {j., an elongation of 

 39-4%; see also A. Scott (1946). For the eflfect of mechanical pressure, 

 see Chambers (1946, 1951). A mathematical treatment of the elon- 

 gation of the Arbacia egg has been made by Buchsbaum and William- 

 son (1943). It will be observed from the photographs (Plate III) that 

 the elongation takes place at telophase (see also Just, 1928 b). A special 

 study of elongation at cleavage in Echinus esculentus has been made by 

 Gray (1931, p. 194). 



1. AsYNCHRONY IN ClEAVAGE 



It will be noticed from the schedule of development (Table 2) and 

 from the photographs that there is an asynchrony in cleavage begin- 

 ning after the 8-cell stage, when one quartet (vegetal) divides horizon- 



