290 Proceedings of the Boyal Physical Society, 



take place, I am speechless. I do not, however, .suppose 

 that they are more mysterious than chemical action. In 

 both we see a rearrangement of the particles of matter in 

 obedience to some fixed laws. So also in embryology, there 

 is a rapid building-up of materials under influences that are 

 common in the organic world, the result of which is to pro- 

 duce animals nearly similar to their parents. I emphasise 

 the qualification, because it is on the acknowledged fact that 

 no two animals, even when born of the same parents, are 

 exactly alike, that Mr Darwin founded his famous theory of 

 the origin of species. This genetic source of variation must 

 not be confounded with modifications induced by the environ- 

 ment. I was very much struck by some recent observations 

 on this subject by Professor Sedge wick in his presidential 

 address at the Zoological Section of the British Association 

 at Dover (1899). " Organised beings/' he writes, " present, as 

 you are aware, two main kinds of reproduction — the sexual 

 and the asexual. These two kinds of reproduction present 

 certain differences, of which the most important and the 

 only one which concerns us now, is the fact that genetic 

 variation is essentially associated with sexual reproduction, 

 and is rarely, if ever, found in asexual reproduction. In 

 other words, whereas the offspring resulting from asexual 

 reproduction as a rule exactly resemble the parent, they are 

 always different from the parents in sexual reproduction." 

 In illustration of this point, he instances what takes place in 

 the potato-plant. The potato — say Magnum Bonum — can 

 and does normally propagate itself asexually by means of its 

 underground tubers. Now, if you take one of these and 

 plant it, it gives rise to a plant exactly resembling the 

 parent. But if, on the other hand, you try to raise plants 

 from the real seeds which are produced in the flowers, " do 

 you think," asks the professor, " that any of them will be the 

 Magnum Bonum, with all its properties of keeping, resisting 

 diseases, and so forth ? Not a bit of it. The probability is 

 that not one of your seedling plants will exactly reproduce 

 the parents." Of course, in the higher animals there is no 

 asexual reproduction, but the point is interesting as showing 

 greater latitude of variation in sexual descent. 



