OF EXPERIMENTAL WORK 223 



Cell Division. — Explained by change in surface tension (R. S. Lillie, 1903, 1909; 

 McClendon, 1910b; see Wilson's The Cell, 1925, p. 158, 192-197 for general refer- 

 ences and discussion; also Gray, 1931, p. 214). 



For interfacial tension, oil-protoplasm, oil-water, see under Oil, references to 

 Chambers and Kopac. 



Other Species and Reviews 



Danielli, 1942, Bourne's Cytology and Cell Physiology. Review. 

 E. N. Harvey, 1954. Protoplasmatologia. Review. 

 E. N. Harvey and Danielli, 1938. Review. 

 Vies, '1926. Paracentrotus lividus. 



TWINS, TRIPLETS, QUADRUPLETS 



Twins, triplets, quadruplets may be produced through destruction of hyaline layer 

 which binds blastomeres together by: 



Shaking. — In Echinus (Driesch, 1891, and later). 



Hypotonic Sea Water. — (Loeb, 1905b, p. 303, translation of 1894 paper). See Just, 

 1939a, p. 13. 



Hypertonic Sea Water. — Just after cleavage is best method. (E. B. Harvey, 1940 a). 

 (Plate XVI, Photograph 8). 



MgCl^. — Added to sea water (Loeb 1900 a). 



Lack of K. — Na or Ca in sea water, in S. purpuratus, (Loeb, 1909b, 191 2, p. 204). 



Ethyl Urethane. — (0.2 M) 3 to 60 min. then sea water and fertilize; fertilization 

 membrane pinches the egg into two parts (E. B. H. unpub.). 



Centrifuging. — In 2-cell stage, in Ps. microtuberculatus (E. B. Harvey, 1935b); in 

 Arbacia (1940 a). Hyaline layer is removed by centrifugal force. 



Each twin has two micromeres (E. B. H. unpub.). 



Natural twins formed in Prionocidaris baculosa by separation of first two blastomeres 

 which develop separately into half sized larvae. (Mortensen, 1938, p. 14). 



Twins, triplets and quadruplets from a single egg may all develop into perfect 

 dwarf plutei (E. B. Harvey, 1940a). Plate XVI, Photograph 8. 



ULTRASONIC WAVES 



High frequency sound waves on Arbacia punctulata eggs (E. N. Harvey, E. B. Harvey, 

 and A. L. Loomis, 1928; E. N. Harvey, 1930). High speed photographs show eggs 

 can be cytolysed in less than 1/1200 second (E. N. Harvey and Loomis, 193 1). 



Other Forms 

 Schmidt, F. O., 1929, California starfish. 



ULTRAVIOLET LIGHT 



Cleavage and Development (Eggs or Sperm Radiated). — Delayed cleavage and ab- 

 normal development (Child, 1924, p. 109 footnote; Hinrichs, 1926b, c, 1927; Nebel, 

 E. B. Harvey, and HoUaender, 1937; E. N. Harvey, 1942; Giese, 1946). Delayed 

 cleavage and enhanced recovery with visible light (Blum, et al., 1949 a, b, 1950 a, 

 c, d, 1 951; Marsbak, 1949 b, c). Of centrifuged eggs. Delay greater if irradiated 

 through oil cap, less if through pigment (C. V. Harding and Thomas, 1950). Of 

 half-eggs. Delay in cleavage of white halves; and of red (non-nucleate) halves ex- 

 cept when exposed before fertilization, to wave lengths of 2700-3130 A (Blum, 

 et al., 1949a, 195OC, d, 1951). Photorecovery of white halves (Blum, et at., 1949a, 

 1 950 c, d, 1951 ; Marshak, 1949 b, c). 



