OF EXPERIMENTAL WORK . 187 



INFRARED LIGHT 



No experimental data for Arbacia punctulata, but in Strongylocentrotus franciscanus and 

 purpuratus, fertilizability decreased with wave lengths 0.8 to 1.2 [jl (Nelson and S. C. 

 Brooks, 1933). 



Photographs of eggs, half-eggs, and nuclei oi A. punctulata with infrared light (E. B. 

 Harvey and Lavin, 1951a, b). 



Reference 

 Giese, 1947. General on radiations. 



INFERFACIAL TENSION 



Oil-Protoplasm; Oil-Water. See under Oil (Coalescence) 



INTRAVITAM DYES 



See Vital Dyes 



JELLY LAYER 



Definition. A gelatinous layer on the outside of the egg, often called the zona pellucida 

 or chorion (Plate XVI, Photograph 3 and Figs 9, 10). Observed in Echinus esculentus 

 by Derbes in 1847, and called by him la couche mucilagineuse. Funnel-shaped micropyle 

 p.^esent in jelly. 



Visibility. — Not visible in sea water because of its refractive index, but its presence 

 is indicated by the spacing between individual eggs. If eggs are contiguous, there is 

 no jelly. Jelly and micropyle can be demonstrated by India or Chinese ink (old 

 method of Boveri, 1901), or squid ink. The jelly is readily shown by a slight tinge to 

 the sea water of Janus green or toluidin blue (cause shrinkage after some minutes) ; 

 also by the halo of sperm caught in the jelly after a heavy insemination. It has been 

 described as radially striated as it comes from the ovary, then becoming invisible 

 (McCIendon 1914a); as a fibrillar network (Chambers, 1933). 



Thickmss. — Is 28 to 32 \l; the average volume ca. 1,050,000 [x^. It swells to 60 (x 

 with squid ink (E. B. H.). The jelly of Pi. miliaris has been found to swell to double 

 its width with rabbit serum and certain amino acids (Runnstrom, Monne, and 

 Wicklund, 1946), and also with versene (Borei and Bjorklund, 1953) ; this also caused 

 swelling of the Lytechinus egg jelly (Tyler, 1953). For the chemistry of squid ink, see 

 Ball and Ramsdell (1940). i* % 



Specific Gravity. — Lighter than the egg, goes to centri^'^ral pole on centrifuging 

 (Shapiro, 1935c; E. B. H. unpub.) (Plate XVI, Photograph 4). 



Presence. — In oocytes as well as mature eggs (F. R. Lillie, 19 14, 19 19, p. 119). Not 

 present in oocytes under 60 fx diameter and may remain till hatching (E. B. H.). 



Not necessary for fertilization membrane (F. R. Lillie, 1914, 1915a; R. N. Harvey, 

 1914, et al.). Some early observers thought it necessary (McCIendon, 191 1, 1914a). 

 See F. R. Lillie and Just, 1924, p. 453, footnote. 



Electric Charge. — Negative, is acidic (McCIendon, 191 i, 1912b). For more recent 

 work see Runnstrom, Tiselius, and Vasseur (1942). 



Permeability changes. — No effect (R. S. Lillie, 191 7). 



Loss of Jelly. — On standing in sea water (many observers). Loss of jelly with age 

 (R. S. Lillie, 191 7; Goldforb, 1918a, b; et al.). 



Not Replaced. — When removed (R. S. Lillie, 192 1 ; et al.). 



Contains Agglutinins. — (Fertilizin), but not in immature eggs (F. R. Lillie, 1914, 

 1915a, 1919, p. 117, etc.; Glaser, 1914b; Loeb, 1915a; Frank, 1939; et al.). For 



