The Theory of Evolution 229 
generations would soon lead to the production of a large number 
of individuals of the new type. The possibility of the forma- 
tion of a new species in this way is clearly shown. . The pro- 
portion of individuals belonging to the new and to the old type 
varies greatly in different forms, and there appears to be a curi- 
ous relation between the type produced and the sex of the indi- 
vidual, but with this question we are not here concerned. A 
single example will suffice to illustrate the character of the result. 
The moth Aglia tau produces an aberrant form, A.lugens. A 
cross between the two types produced 14 males and 28 females 
of A. tau, and 31 males and 13 females of A. lugens. Two indi- 
viduals (F;) of the type A. lugens belonging to the second genera- 
tion (F,) were mated. They produced 3 males and 8 females 
of A. tau, and 49 males and 42 females of A. lugens. The results 
do not appear to conform to the Mendelian law, but it is not 
improbable that the aberration was not a pure form but a domi- 
nant-recessive. However this may be, the appearance of both 
types and the absence of intermediate grades is of the highest 
interest. 
Standfuss’s general conclusion is given in the following state- 
ment: A union between the parent species and an aberration 
that has arisen suddenly and discontinuously (‘‘sprungweise’’) 
— a variety in the technical sense — produces in many cases not 
any intermediate forms, but the parental species type and that of 
the aberration. On the other hand, a union between the parent 
species and an individual of a local race showing a series of inter- 
mediate gradations produces a series of intermediate forms.’ 
If the new character is transmitted to all of its hybrid offspring 
and to their descendants, it will become sooner or later trans- 
ferred to all of the individuals that are met with, and in time may 
become a part of the common inheritance. 
It remains only to consider another point — one on which 
de Vries has recently laid some emphasis. He finds in the even- 
ing primrose that the new progressive mutations are to some 
1 Of another combination, however. 
2 This is the case apparently in the crosses described by Tutt. 
