260 
parental form in a general way, even down to very minute 
characteristics which may be peculiar to the parent as an 
individual. 7 
Theoretically, then, it may be assumed that like ought to 
produce like, for after all the offspring, whether the product of 
fission or of sexual union, is but a detached portion of the 
parent ;* and according to Darwin’s theory of pangenesist there 
is no real distinction between reproduction by fission or 
by sexual union—the latter is only the former more specialized. 
When, however, the new organism is in the smallest 
degree unlike its parent it can be assumed that the failure of 
“like to produce like” is due to some change of environment 
affecting either the parent or the offspring. It may then be 
supposed that “like produces like if the conditions of environ- 
ment be absolutely and continuously uniform;” but since the 
conditions of environment never do absolutely conform to these 
requirements, and sometimes very widely depart from them, it 
may be said that “like produces like so far as the conditions of 
environment will allow.”{ The differences between parent and 
offspring may, then, be presumed to depend on the greater or less 
diversity of environment, and the greater or less susceptibility 
of the organism.§ It follows from this that there is more 
[*The phenomena of alternation of generations do not conflict with this state- 
ment. Neither in homogenesis nor in heterogenesis is the offspring at once like 
its parent—it only becomes like by passing through successive cycles of changes 
similar to those by which its parent was produced. The correspondence of the 
cycles of the offspring to those of the parent fulfil the statement of “like 
producing like.’’] 
[tIn his “Essays on Heredity,” Weismann rejects Darwin’s theory of 
Pangenesis. It may be a faulty theory ; but it seems to fit in very intelligibly 
with observed facts. The consideration of this matter must be left over for the 
present. ] 
[{ Professor Harker remarked to me that the little difference in the species 
of the genus Lingula from the Cambrian to the present day might be ascribed to 
the practical uniformity of pelagic conditions.] 
§ And in the product of sexual union the heterogeneity of the parents would 
be another factor. 
