768 REPORT—1899. 
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 domestication (‘ Variation,’ ii. 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 moditied without the aid of selection,’ 
It is, however, as I have said, extremely doubtful if variations of this kind 
really occur. The appearance of them may be caused by the combination of the 
two other kinds of variation. 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. 
Moreover, a general consideration of the facts of the case renders it improbable 
that such similar and definite genetic variations should often occur, at any rate 
in sexual reproduction. For although the effect upon the reproductive organs 
may possibly 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. 3: Are 
genetic variations ever found in asexual reproduction ? 
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, avd 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 repro- 
duction, 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—he transmitted in asexual reproduction? Now 
we have already seen that the etlect of external agencies acting upon the organism 
must be regarded under: two heads, according 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 
} Weismann, On Heredity, vol. ii. English edition, p. 161. Warren, E. ‘ Observa- 
tion on Heredity in Parthenogenesis,’ Proc. Roy. Soc. 65, 1899, p. 154. These are the 
only observations I know of on 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 Weismann’s view that Cypris reptans, 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 seena 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 vety rare and only appears after long intervals. 5 
