762 REPORT—1899. 
In sexual reproduction then, in addition to the real reproductive act, which is 
the division by fission of the parent into two unequal parts, the one of which con- 
tinues to be called the parent, while the other is the gamete, there is thesubsequent 
conjugation process. It is to this conjugation process that that important con- 
comitant of sexual reproduction must be attributed, namely genetic variation. We 
have thus traced genetic variation to its lair. We have seen that it is due to the 
formation of a new individuality by the fusion of two distinct individualities. We 
have also seen that in the higher animals it is always associated with the repro- 
ductive act. 
Let us now take a wider survey and endeavour to ascertain whether this most 
important process, a process upon which depends the improvement as well as 
the degradation of races, ever takes place independently of the reproductive act. 
In the Metazoa,to which for our present purpose I allude under the term higher 
animals, conjugation never takes place except in connection with reproduction. It is 
impossible from the nature of the process that it should do so, as I hope to explain 
later on. But among the Protozoa, the simplest of all animals, it is conceivable 
that conjugation might take place apart from reproduction, and as a matter of 
fact it does do so, Let us now examine a case in which this occurs. Amongst 
the free-swimming ciliated Infusoria it frequently happens that two individuals 
become applied together, and that the protoplasm of their bodies becomes con- 
tinuous. They remain in this condition of fusion for some days, retaining how- 
ever their external form and not undergoing complete fusion. While the continuity 
lasts there is an exchange of living substance between the two bodies, in which 
exchange a bit of the nucleus of each participates. It thus happens that at the 
end of conjugation, when the two animals separate, they are both different from 
what they were at the commencement; each has received protoplasm and a 
nucleus from its fellow, and the introduced nucleus fuses, as we know, with the 
nucleus which has not moved. It would therefore appear that all the essential 
features of the conjugation process, as we learnt them in the case of the conjuga- 
tion of the gametes in the Metazoa, are present, and it is impossible to doubt that 
we have here an essentially similar phenomenon. The phenomenon differs, how- 
ever, from the conjugation first described in this interesting and important respect, 
that the two animals separate and resume their ordinary life. It is true that 
their constitution must have been profoundly changed, but they retain their general 
form. I say that the constitution of the exconjugates, as we may call them after 
they are separated, must be different from what it was before conjugation, but so far 
as I know no difference in structure corresponding with this difference in con- 
stitution has been recorded. I feel no sort of doubt, however, that structural 
differences, z.e. variations, will be detected when the exconjugates are closely. 
scrutinised and compared with the animals before conjugation, and [ would suggest 
that definite observations be made with a view to testing the point. Here then 
we have a case of conjugation entirely dissociated from reproduction, Other cases 
of a similar character are known among the Protozoa, though as a general rule the 
fusion between the conjugating organisms is complete and permanent. Among 
plants conjugation is generally associated with reproduction, but not always; for.in 
certain fungi * fusion of hyphe and consequent intermingling of protoplasm occurs, 
and is not followed by any form of reproduction. Among bacteria alone, so far as 
I know, has the phenomenon of conjugation never been observed. 
To sum up, we have seen that the phenomenon of conjugation is very widely 
distributed. Excluding the bacteria, there is reason to believe that it forms a 
part of the vital phenomena of all organisms. Its essential features are a mixture 
and fusion of the protoplasm of two different organisms, accompanied by a fusion 
of their nuclei. It results in the formation of a new individuality, which differs 
from the individualities of both the conjugating organisms. This difference 
manifests itself in differences in habit, constitution, form, and structure; such 
differences constituting what we have called genetic variations. 
? It must be mentioned, however, that in the case of these fungi the fusion of 
nuclei has not been observed, nor has it been noticed whether the habit, structure, 
or constitution of the conjugating plants is altered after the fusion. 
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