DEVELOPMENT IN ARBACIA. I5I 



Control normal; all eggs with fertilization membranes in 3 to 5 

 minutes. Experimental eggs examined at irregular intervals 

 throughout the day, but no increase in the number of membranes. 



Whether the appearance of a fertilization membrane, and im- 

 pregnation itself will fail to take place in other eggs under similar 

 conditions cannot be predicted, and is perhaps even improbable. 

 With the eggs of Arbacia punctulata however I repeated these 

 tests so often that I cannot doubt the correctness of my obser- 

 vations, and I therefore fail to understand Kite's^ claim that he 

 succeeded in calling forth a fertilizatioil membrane in this egg 

 by means of a single spermatozoon. I imagine that his method 

 involved factors whose importance was unsuspected, since he 

 says: "The real difficulty with this type of experiment is not the 

 size of the spermatozoon, but the fact that when four or five are 

 injected into the egg-jelly, they usually swim out and away from 

 the egg. This necessitates the making of many injections in 

 order to get a single spermatozoon to attach itself to the vitelline 

 membrane and start the reaction." The "making of many 

 injections" very likely involves touching the vitelline membrane 

 an equal number of times, which recalls an experiment men- 

 tioned in my earlier paper^ in which fertilization membranes were 

 induced by surrounding the eggs with large numbers of minute 

 infusoria. Observation indicated a continuous bombardment of 

 the ova. 



A quantitative relation between the rate of appearance of the 

 membrane and the agencies, spermatozoa, normally calling it 

 forth is really no more surprising than the efficacy of Ca as an 

 inhibitor. Since now sea-water of sufficient hypotonicity will of 

 itself call forth membranes^ one may expect the exact reverse of 

 the Ca-experiments if one immerses the eggs briefly in hypotonic 

 solutions. Such ova, if not submerged too long so that the 



1 G. L. Kite, "The Nature of the FertiHzation Membrane of the Egg of the Sea 

 Urchin {Arbacia -punctulata)," Science, Vol. XXXVI., pp. 562-564. 



2 Science, loc. cit. 



3 In my preliminary communication {Science, loc. cit.) I considered the method of 

 "inducing" a fertilization membrane in Arbacia by means of hypotonic sea-water 

 new. Schiicking however described this procedure in the year 1903. {Arch. f. 

 d. ges. Physiol., Vol. 97, p. 85.) The same method was used on Arbacia eggs by 

 McClendon in 1910. {American Journ. Physiol., p. 246.) 



