346 LEWIS V. HEILBRUNN. 



which the membrane is thrust out is but one of the difficulties 

 which such a theory would have to surmount. Traube 1 con- 

 siders artificial membrane elevation as the result of a secretion 

 after a return to normal sea-water, but in all but a few cases, 

 such a return to sea-water is not necessary. McClendon 2 is of 

 the opinion that an electro-positive (or acid) colloid secretion 

 is 3 poured out from the egg which reacts with the supposedly 

 electro-negative chorion to produce the vitelline membrane. 

 This view is, of course, not in accord with the evidence cited 

 above in favor of the preexistence of a vitelline membrane. 

 Elder 4 has recently adopted a conclusion identical with that of 

 McClendon, to whom, however, he makes no acknowledgment. 

 He states that the vitelline membrane does not "form" on eggs 

 which lack a chorion. But these eggs are evidently not in good 

 condition, they are probably overripe, and such eggs have been 

 shown by Fol and Loeb incapable of pushing out a vitelline 

 membrane. Elder also states that if the chorion be removed, 

 membrane elevation does not occur (a fact previously claimed 

 by McClendon) but his method of removal involves keeping the 

 eggs 12-14 hours in artificial sea-water. This, of course, pre- 

 cludes membrane elevation. Such evidence is directly contro- 

 verted by the fact observed by Lyon 5 that after a most vigorous 

 treatment in the centrifuge normal membrane elevation occurs. 

 In eggs treated in this manner the chorion is always absent. 



Fol 6 in discussing membrane elevation in Asterias eggs, a 

 process which he states is exactly similar to membrane elevation 



1 J. Traube, Biochem. Zeitsch., XVI., 182 (1909). 



2 J. F. McClendon, BIOL. BULL. XXII., 157 (1912). 



3 As proof that this colloid, which is assumed to lie directly beneath the mem- 

 brane after fertilization, is electro-positive, McClendon states that the passage of 

 an electric current through fertilized eggs in sea-water causes the membrane to 

 "bulge out" towards the cathode. This effect, however, may very well be due to 

 an attempted migration of the egg in the direction of the anode, towards which 

 electrode, most if not all cells migrate (probably because of the alkalinity of proto- 

 plasm). The fact that eggs which have ruptured their membranes do not migrate 

 to the anode (McClendon, Amer. Journ. Physiol., XXVII., 273 (1910)) is probably 

 due to a retarding action of the film of water adjoining the glass slide (see W. B. 

 Hardy and H. W. Harvey, Proc. Roy. Soc., B. LXXXIV., 217 (1911)). 



4 J- C. Elder, Arch. f. Ent.-Mech., XXXV., 145 (1912). 

 6 E. P. Lyon, Arch. f. Ent. Mech., XXIII., 151 (1907). 

 6 Loc. cit. 



