D.—ZOOLOGY. 81 
farther back, for we must still account for their origin and diversity. 
- The same objection applies to the suggestion that the complex of 
factors alters by the loss of certain of them. To account for the 
progressive change in the course of evolution of the factors of in- 
heritance and for the building up of the complex it must be supposed 
that from time to time new factors have been added; it must further 
be supposed that new substances have entered into the cycle of 
metabolism, and have been permanently incorporated as_ self- 
propagating ingredients entering into lasting relation with pre-existing 
factors. We are well aware that living protoplasm contains molecules 
of large size and extraordinary complexity, and that it may be urged 
that by their combination in different ways, or by the mere regrouping 
of the atoms within them, an almost infinite number of changes may 
result, more than sufficient to account for the mutations which appear 
But this does not account for the building up of the original complex. 
If it must be admitted that such a building process once occurred, what 
right have we to suppose that it ceased at a certain period? We are 
_ driven, then, to the conclusion that in the course of evolution new 
* 
material has been swept from the banks into the stream of germ-plasm. 
If one may be allowed to speculate still further, may it not be 
supposed that factors differ in their stability ?—that whereas the more 
stable are merely bent, so to speak, in this or that direction by the 
environment, and are capable of returning to their original condition, 
as a gyroscope may return to its former position when pressure is 
removed, other less stable factors may be permanently distorted, may 
have their metabolism permanently altered, may take up new substance 
from the vortex, without at the same time upsetting the system of 
delicate adjustments whereby the organism keeps alive? In some such 
way we imagine factorial changes to be brought about and mutations 
to result. 
Let it not be thought for a moment that this admission that factors 
are alterable opens the door to a Lamarckian interpretation of evolution | 
According to the Lamarckian doctrine, at all events in its modern form, 
a character would be inherited after the removal of the stimulus which 
called it forth in the parent. Now of course, a response once made, 
a character once formed, may persist for longer or shorter time accord- 
ing as it is stable or not; but that it should continue to be produced 
when the conditions necessary for its production are no longer present 
is unthinkable. It may, however, be said that this is to misrepresent 
the doctrine, and that what is really meant is that the response may 
so react on and alter the factor as to render it capable of producing the 
new character under the old conditions. But is this interpretation any 
more credible than the first ? 
Let us return to the possible alteration of factors by the environ- 
ment. Unfortunately there is little evidence as yet on this point. In 
the course of breeding experiments the occurrence of mutations has 
repeatedly been observed, but what led to their appearance seems never 
to have been so clearly established as to satisfy exacting critics. Quite 
lately, however, Professor M. F. Guyer, of Wisconsin, has brought 
forward a most interesting case of the apparent alteration at will of a 
