256 W. WALDEYER. 
plasma”? eliminated from any given egg-cell is not always 
equal to that eliminated by any other egg-cell of the same 
parent ; at any rate it is not necessarily so. 
Let us therefore suppose in one mother the formula of the 
Keimplasma to be a+a,+0+06,+¢+¢,+d+d,+e+e,4+f4+f ; 
all the eggs produced by her will have a Keimplasma of this 
composition. Suppose three of her eggs are fertilized, and 
from them three offspring arise, by means of spermatozoa 
whose Keimplasma formula is 0+0,+p+p,+9+q, (it need not 
be of the same generation as that of the egg; it may therefore 
have a less complicated constitution). From the first egg, then, 
a second directive corpuscle might be extruded, with a formula 
a+b+c+d+e+f; from the second egg, one having a formula 
a,+6,+¢,+d,+e,+f,; from the third, one with the formula 
at+ta,t+ce+ce,+d+d,. Then, after fertilization, the three eggs 
would have a Keimplasma of equal dignity, according to the 
grade of composition, but not of equal kind of composition, as 
appears thus: 
Egg Lath+¢4+4,+4+/A+0+9+ptatgtn 
Egg Il. a+d+e+d+et+/f+toto+pt+p+9+4: 
Egg HI. 6+4+e+et+f+fAtoto+t+pt+pyt+qtn 
Weismann comes to the conclusion that by this means may 
perhaps be explained the variations (individuality) which, 
according to experience, the offspring of one and the same 
pair of parents exhibit. He also remarks on the relations of 
twins. It happens, as is well known, that twins may be so 
much alike as to be mistaken for one another. For these, 
the origin from one egg must be taken as probable, whereas 
other twins, which do not resemble one another, owe their 
origin probably to eggs fertilized at the same time. Weismann’s 
idea is exceedingly suggestive, and allows of many applica- 
tions. One example may again be pointed out. He explains 
why in parthenogenetic eggs only one directive corpuscle is 
extruded, since this does not consist of the “ Ahnenplasma,” 
which is removed only by the second directive corpuscle. 
Weismann, and before him Strasburger and Hensen (90), 
have called attention to a matter which offers an insuper- 
