408 Ralph S. Lillie 



those warmed at periods of lo to 15 minutes after removal; after 

 an hour (at which time most mature eggs had formed polar bodies) 

 the proportion of immature eggs that formed membranes had 

 declined considerably, and at later stages only a few were formed. 

 This is not in the least an isolated observation, but is fairly typ- 

 ical of what I have frequently observed; the ability of immature 

 eggs to form membranes seems in general best marked shortly 

 after removal, and diminishes after an hour or more in sea-water. 

 An observation made on the same lot of eggs showed that sperma- 

 tozoa may also induce membrane-formation in immature eggs; 

 sperm was added at i h. 25 m. after removal; the next morning 

 a fair proportion of the mature eggs had formed larvae; and nearly 

 all of the immature eggs showed perfectly typical sharply defined 

 fertilization-membranes; otherwise these eggs remained unchanged. 

 Spermatozoa are known to enter immature starfish-eggs, ^° but 

 typically to produce no membranes. Under certain conditions 

 however, not definitely understood (eggs "over-ripe" or otherwise 

 not quite normal), membranes may be formed as just seen, either 

 by spermatozoa or through an artificial agency. The explanation 

 may be as follows: normally the possibility of membrane-forma- 

 tion depends on the passage of certain substances from the nucleus 

 to the cytoplasm, since the beginning of maturation is a prerequi- 

 site; in the above eggs however the permeability of the germinal 

 vesicle membrane is abnormal, so that the substances necessary 

 to the membrane-formation, which ordinarily are unable to tra- 

 verse the nuclear membrane, are now able to effect this passage 

 and to enter the cytoplasm. The latter then reacts to heat or the 

 entrance of the spermatozoon by forming a membrane in the man- 

 ner characteristic of mature eggs. 



It is interesting also to note that such immature eggs show no 

 other change in their properties; they remain clear and unaltered 

 for prolonged periods and show no greater tendency to disinte- 

 grate than do normal immature eggs — a fact apparently contra- 

 dictory of Loeb's view that the separation of the membrane in- 

 volves an acceleration of oxidative processes in the egg. In mature 



3° Wilson and Mathews: Journal of Morphology, x, p. 319, 1895. 



