208 ALPHABETICAL COMPILATION 



PHOTODYNAMIC ACTION 



See Visible Light 



PIGMENT GRANULES 



See Chromatophores, Echinochrome 



PLASMA MEMBRANE 



Definition. — Plasma membrane is the membrane at the surface of the protoplasm,* 

 over the cortical layer, supposed to be responsible for the permeability of the cell. 

 The older investigators made no distinction between plasma membrane and vitelline 

 membrane, calling the two together the "pellicle." It is difficult to distinguish the 

 two optically in an unfertilized Arbacia egg. It has been called the "luminous" layer 

 by Runnstrom and Monne (1945 a) in Psammechinus miliaris, since it is luminous in 

 dark field. See Figs 9 and 10. 



Thickness. — Less than 10 mpi (Danielli, 1942, 1951b, p. 154). The dried plasma 

 membrane of the red blood cell is 50-60 A (Parpart and Ballentine, 1952; Hillier 

 and Hoffman, 1953). 



Structure. — A liquid film (Chambers, 1935b, 1938b, 1944, 1949). Fatty (Chambers, 

 1935b). Lipoid with adsorbed protein (E. N. Harvey and Danielli, 1938; Danielli 

 1951b, p. 151; Davson and Danielli, 1952, p. 57). 



Oil Coalescence. — Coalescence of egg with oil drops on the surface (Chambers, 

 1935b, 1944; Chambers and Kopac, 1937a; Kopac and Chambers, 1937; Kopac, 

 1940a, 1943; etc.). 



Other Properties. — Very delicate, easily ruptured, becomes more fluid on churning 

 with needle and with calcium ; cannot be removed ; is necessary for life of cell ; can 

 repair itself (Chambers, 1938 b, 1940, 1944, 1949, 1950; Kopac, 1940 a). 



Other References (General) 



Just, 1939 b. The Biology of the Cell Surface. 

 Runnstrom, 1949 a. 



POLYSPERMY 



Definition. — Polyspermy is the fertilization of an egg by two or more sperm, the egg 

 dividing into three or more cells at first cleavage. 



Historical. — Observed by Fol(i877) and studied byO. and R. Hertwig (1887) in 

 Paracentrotus lividus. A good account of the early work of the Hertwigs, Boveri (1902, 

 1907), etc. is given in Morgan's (1927) Experimental Embryology, Chapt. VII. It was 

 concluded that "in the sea urchin the division of the protoplasm is strictly regular, 

 but the chromosomal distribution is disturbed" (p. 87) and "swimming blastulae 

 develop from these eggs, but only very rarely a normal embryo" (p. 86). See also 

 Wilson's (1925). The Cell, p. 416 and 917. 



Occurs. — In Arbacia in unripe eggs fertilized soon after the extrusion of the second 

 poiar body (E. B. H.). See Part II, Chap. 10, sect. g. 



Caused. — In Arbacia by Stale eggs, i.e., eggs left standing in sea water (Hoadley 

 1923; J. M. Clark, 1936, after 16 hours). Shaking (Morgan, 1893, 1895b). Cold 



* Recent investigations of A. K. Parpart and P. C. Laris with a television microscope, 

 indicate that the plasma membrane of the unfertilized Arbacia egg lies inside the cortical, 

 layer which is between the vitelline membrane and the plasma membrane {Biol. Bull. 

 107 : 301, 1954). 



