SErTEMBER 21, 1899] 
NATORE 
597 
after the lapse of some generations. On this point Darwin 
says: “‘ Universal experience shows us that when new flowers 
are first introduced into our gardens they do not vary; but 
ultimately all, with the rarest exceptions, vary to a greater or 
less extent” (‘* Variation,” 2, p. 249)! With regard to the 
variability thus induced, it is to be noticed that it is not confined 
to any particular organ, nor does it show itself in any particular 
way. On the contrary, the whole organisation is affected, and 
the variations are quite indefinite. 
To sum up the argument as it at present stands: (1) a change 
in conditions cannot affect the next generation unless the repro- 
ductive organs are affected ; (2) from a consideration of the facts 
of the case, it is almost inconceivable that the effect produced 
upon any organ of a given organism by a change of conditions 
should so modify the reproductive organs of that organism as to 
lead to a corresponding modification in the offspring without the 
latter being exposed to the same conditions ; (3) the only effects, 
which are certainly known, of changed conditions upon the 
reproductive organs are (a) the production of sterility ; (4) an 
increase in genetic variability. 
As far, then, as our certain knowledge goes, it would appear 
that a change of conditions may have one or both of the 
following effects :— 
(1) A definite change, of the same character, or nearly so, in 
all the individuals acted upon. Such changes may be adaplive 
or non-adaptive, but they are not permanent, lasting only so 
long as the change of conditions, or at most during the life of 
the individual acted upon. They are not transmitted in repro- 
duction, and do not appear in the offspring unless it is sub- 
mitted to the same conditions. These variations are the direct 
result of the action of the environment upon the individual, with 
the exception of the reproductive organs. 
(2) Increase in the variations of the genetic kind These are 
seen, not in the generation ? first submitted to the changed con- 
dition, but in the next or some subsequent generations. The 
effect is produced through the reproductive organs. These 
variations are non-adaptive, and different in each individual. 
If the reproductive organs are affected we get an increase in 
the variations of the genetic kind. These, we have seen, are 
usually of an indefinite character ; they are different in every 
case, and their nature cannot be predicted from experience. But 
we still have to ask: Is this is a universal rule? Does it never 
happen that a change of conditions so affects the reproductive 
organs as to produce a definite non-adaptive change of the same 
character or nearly so in all the descendants of the individual 
acted upon? This is the most obscure question connected with 
the study of variations. If such changes occur, they might be 
cumulative, being increased in amount by the continued action 
of the conditions. They would be non-adaptive, their nature 
depending on the constitution of the reproductive cells and 
having no functional relation to the original stimulus. 
As possible examples of such variation, I may recall those 
variations referred to by Darwin as ‘fluctuating variations 
which sooner or later become constant through the nature of the 
organism and of surrounding conditions, but not through natural 
selection” (‘ Origin,’ ed. 6, p. 176); to the variations in 
turkeys and ducks which take place as the result of domestic- 
ation (‘‘ Variation,” 2, p. 250); to those variations which 
Darwin had in his mind when he wrote the following sentence 
(‘* Origin,” p. 72): ‘‘There can be little doubt that the 
tendency to vary in the same manner has often been so strong 
that all the individuals of the same species have been similarly 
modified without the aid of selection.” 
It is, however, as I have said, extremely doubtful if vari- 
ations of this kind really occur. The appearance of them may 
be caused by the combination of the two other kinds of vari- 
ation. In all cases which might be cited in support of their 
occurrence, there are the following doubtful elements: (1) no 
clear statement as to whether the variations showed themselves 
in the individuals first acted upon; (2) no history of the 
organisms when transported back to the old conditions. 
1 The phenomenon of increased variability following upon change or con- 
ditions has most often been observed when the change has been from a state 
of nature to a state of cultivation. Hence the conclusion has been drawn 
that the kind of change involved in domestication alone induces variation. 
But there is no evidence in favour of this view. The evidence shows that 
change of conditions in itself may induce greater variability. 
2 No doubt the individuals of the generation first submitted to the 
changed conditions would be affected as regards their reproductive organs, 
which would be altered in structure, but this has not been made out, 
though there are indications of such an effect in certain plants, vide 
Appendix. 
NO. 1560, VOL. 60] 
Moreover, a general consideration of the facts of the case 
renders it improbable that such similar and definite genetic 
variations should ofien occur at any rate in sexual reproduction. 
For although the effect upon the reproductive organs may pos- 
sibly be almost the same in nearly all the individuals acted upon, 
it must not be forgotten that the reproductive elements have to 
combine in the act of conjugation, and that it is the essence of 
this act to produce products which differ in every case. 
Effect of Changed Conditions in Asexual Reproduction. 
This brings us to the consideration of the question reserved on 
p- 503: Are genetic variations ever found in asexual reproduc- 
tion? 
If the views expressed in the earlier part of this address are 
correct, it would seem to follow that genetic variations are 
variations in the actual constitution, and are inseparably 
connected with the act of conjugation. The act of conjugation 
gives us a new constitution, a new individuality, and it is the 
characters of this new individual in so far as they differ from the 
characters of the parents which constitute what we have called 
genetic variations. According to this, the answer to our 
question would be that genetic variations cannot occur in 
asexual reproduction, and that if any indefinite variability 
recalling genetic variability makes its appearance! it must be 
part of the genetic variability and directly traceable to the 
zygote from which the asexual generations started. 
But if genetic variability is not found in asexual reproduction, 
the question still remains, Can the other kind of variations— 
namely, those due to the direct action of external forces upon 
the organism—be transmitted in asexual reproduction? Now 
we have already seen that the effect of external agencies acting 
upon the organism must be regarded under two heads, accord- 
ing as to whether the reproductive organs are or are not 
affected. If the reproductive organs are not affected, then 
variations caused by the impact of external forces will not be 
transmitted ; if, on the other hand, they are affected, the next 
generation will show the effect. We have further seen that in 
the case of sexual reproduction a modification of the repro- 
ductive organs will, because of the intervention of conjugation, 
appear as an increase in genetic variability only. How will the 
matter stand in the case of asexual reproduction? First, with 
regard to modifications which do not affect the reproductive 
system—they, as in sexual reproduction, will not be transmitted. 
Secondly, as regards modifications which do affect the repro- 
ductive organs—they will be transmitted, z.¢. they will affect the 
next generation; and the question arises, How will they be 
transmitted ? For here we have the opportunity wanting in the 
case of sexual reproduction of studying the transmission of 
modifications of the reproductive system without the compli- 
cations introduced by the act of conjugation. 
In considering this matter, it must be remembered that the 
reproductive organs are, with regard to external influences, 
exactly as any other organ. They can be modified either 
directly or indirectly, though they are in animals often less 
liable to direct modification by reason of their internal position.* 
These modifications may, as in the case of other organs, be 
obvious to the eye of the observer, or they may be so slight as 
only to be detected by an alteration of function. Now, in the 
case of the reproductive organs this alteration of function will 
show itself in the individuals of the next generation (if not be- 
fore) which proceed directly and without any complication from 
the affected tissue. How will these individuals be affected ? 
Will they all be affected in the same kind of way or will they 
they be affected in different ways? -Finally, will the modi- 
1 Weismann, ‘‘ On Heredity,” vol. ii. English edition, p. 161. Warren 
E., ‘‘Observation on Heredity in Parthenogenesis,” Proc. Roy. Sac., 65, 
1899, p- 154. These are the only observations I know of cn this subject. 
They tend to show the presence of a slight variability, but they are not 
entirely satisfactory. In connection with this matter, I may refer to Weis- 
mann’s view that Cyfa7s veptans, the species upon which his observations 
were made, reproduces entirely by parthenogenesis, and has lost the power 
of sexual reproduction, ‘This view is based on the fact that he has bred 
forty consecutive parthenogenetic generations and has never seen a male. 
As Weismann bases some important conclusions on this view, with regard to 
the importance of conjugation in rejuvenescence of organisms, I may point 
out that the fact that he has bred forty successive generations and has never 
seen a male cannot be regarded as conclusive evidence that males never 
appear. We know of many cases in which reproduction can continue for 
more than forty generations without the intervention of conjugation, e.g. 
ciliated infusoria, many plants, and of other species of crustacea in which 
the male is very rare and only appears after long intervals. 
2 How far the abnormal position of the testes of mammalia may receive its 
explanation in this connection is a question worthy of consideration. 
