Variahility of Eggs and Sperm of Sea-Urchins, 87 



10. In some females the eggs formed fertilization membranes in 

 about 2 minutes, others required 3 to 6 minutes, or formed no mem- 

 branes at all. Rapid membrane formation was associated with small 

 variability of size, globular shape, and high jelly count; slow formation 

 with enlargement or considerable variation in size, high percentage of 

 elliptical eggs and low jelly count. The former were in good, the 

 latter in poor physiologic condition. 



11. The rate of early cleavage and the total cleavage varied most 

 widely. The total cleavage varied from complete sterility to 100 per 

 cent cleavage. High cleavage is correlated with normal size, globular 

 shape, large jelly count, and rapid membrane formation; and vice versa, 

 low cleavage with the opposite conditions. 



12. This amazingly large variation is due to: 



a. A primary, small variability in ripe eggs. 



6. The effect of chemico-physical agencies acting on the ripe eggs within the 

 body of the female. 



c. A variation in time or ripening of different groups of eggs within a given 



female. 



d. The time between maturation and removal of the eggs to sea-water, 



which time may be different for different females. 



e. The differential effect of sea-water upon physiologically different eggs. 



Eggs which have been removed from different individuals at the same 

 time and are of the same chronologic age are not necessarily in the same 

 physiologic condition. The extent of the change may be determined 

 by the study of their variations. 



13. For certain experimental work the eggs should be grouped, not 

 according to age — i. e., the time since removal from the body — but 

 according to their physiologic state, which may be accurately deter- 

 mined by the various tests suggested above. 



BIBLIOGRAPHY. 



1. LiLLiE, F. R. 1914. Studies of fertilization. VI. The mechanism of fertilization in 



Arbacia. Jour. Exper. ZooL, vol. 16, 523. 



2. . 1915. Studies of fertilization. VII. Analysis of variations in the fertilizing 



power of sperm suspensions of Arbacia. Biol. Bull. 28, 228. 



3. LiLLiE, R. S. 1916. Physiology of cell division. VI. Rhythmical changes in resistance 



of dividing sea-urchin eggs to hypotonic sea-water. Joiu". Exper. Zool., vol. 21 , 369. 



4. LoEB, J., and M. M. Chamberlain. 1915. An attempt at a physico-chemical explana- 



tion of certain groups of fluctuating variations. Jour. Exper. Zool., vol. 19, 559. 



5. , and H. Wasteneys. 1915. Further experiments on the relative effect of weak 



and strong bases on the rate of oxidation in the egg of the sea-urchin. Jour. Biol. 

 Chem., vol. 21, 153. 



6. . 1913. Artificial parthenogenesis. 



7. Stockard, C. R. 1913. Experimental study of the position of the optic anlage in 



Amblystoma pundatum, with a discussion of certain eye defects. Amer. Jour. 

 Anat., 15. 



8. Wasteneys, H. 1916. The rate of oxidations in reversed artificial parthenogenesis. 



Jour. Biol. Chem., vol. 24, 281. 



