474 the president's address. 



originally quite separate, and even of different parentage, com- 

 bining to form an individual of a higher order of quite a different 

 nature from any produced by ordinary colony formation. 



Such mixed individuals are rare in a state of nature, but 

 various experiments show that they are quite easily produced 

 artificially in certain cases. We can make mixed or composite 

 individuals by the process of grafting both in plants and animals 

 It is by no means difficult to graft together parts of two hydras. 

 We can even join the hind part of one tadpole to the front part 

 of another, and the product may develop into a complete frog, 

 derived possibly from individuals of two distinct species. 



Modern surgery has enabled us to perform marvellous grafting 

 operations even upon the human subject. A few years ago 

 an account was published of a girl whose knee-joint had been 

 removed and replaced by that of another person, with perfect 

 success. Theoretically, and apart from the difficulties of technique, 

 there seems to be no limit to the possibilities of surgery in this 

 direction. It would almost seem as if the whole organism were 

 made up of a number of interchangeable standard parts, like a 

 bicycle. Suppose it were possible to carry on the process until 

 all the parts of the body had one by one been replaced by others, 

 what would be the result from the point of view of individuality ? 

 Should we be able to say that the same individual still existed 

 after all the operations had been carried through ? It reminds 

 us of the Irishman's knife, that at various times had had all 

 the blades replaced and a new handle, but was still to him the 

 same knife. 



Other experiments have shown that it is possible to produce 

 mixed individuals by joining together embryonic cells or blasto- 

 meres derived from different eggs. Garbowski in 1904 succeeded 

 in uniting blastomeres derived from different embryos of a sea- 

 urchin, either by hydraulic pressure or by squeezing them 

 together by means of glass-headed pins. The fragments of the 

 divided embryos were coloured intravitally with various stains 

 that did not injure them, so that they could be readily distin- 

 guished from one another. Even when the blastomeres were 

 taken from embryos in different stages of development, the 

 composite embryos formed from their union developed into 

 uniform pluteus larvae by means of various regulation processes. 



An American biologist, H. V. Wilson, has shown that if a 



