June 8, 1900.] 



SCIENCE. 



887 



commonly in Arthropods than in other 

 groups, but it may be more common than is 

 supposed.* 



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 continues 

 to be called the parent, while the other is 

 the gamete, there is the subsequent con- 

 jugation process. It is to this conjugation 

 process that that important concomitant 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 al- 

 ways associated with the reproductive act. 



Let us now take a wider survey and en- 

 deavor to ascertain whether this most im- 

 portant process, a process upon which 

 depends the improvement as well as the 

 degradation of races, ever takes place inde- 

 pendently 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 im- 

 possible 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 con- 

 jugation might take place apart from repro- 

 duction, and as a matfer 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 be- 

 comes continuous. They remain in this 

 condition of fusion for some days, retaining 



*It may be mentioned as a curious fact that par- 

 thenogenesis is rarely found in the higher plants, and, 

 as I have said, is not known for the male gamete 

 among animals. 



however their external form and not under- 

 going complete fusion. While the con- 

 tinuity lasts there is an exchange of living 

 substance between the two bodies, in which 

 exchange a bit of the nucleus of each par- 

 ticipates. It thus happens that at the end 

 of conjugation, when the two animals sepa- 

 rate, they are both different from what they 

 were at the commencement ; each has re- 

 ceived 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 learned them in the case of 

 the conjugation of the gametes in the 

 Metazoa are present, and it is impossible to 

 doubt that we have here an essentially simi- 

 lar phenomenon. The phenomenon differs, 

 however, from the conjugation first de- 

 scribed 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 pro- 

 foundly 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 difierence in structure 

 corresponding with this difference in con- 

 stitution has been recorded. I feel no sort 

 of doubt, however, that structural differ- 

 ences, i. e., variations, will be detected 

 when the exconjugates are closely scrutin- 

 ized and compared with the animals before 

 conjugation, and I would suggest that defi- 

 nite 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 simi- 

 lar character are known among the Pro- 

 tozoa, though as a general rule the fusion 

 between the conjugating organisms is com- 

 plete and permanent. Among plants, con- 

 jugation is generally associated with repro- 



