REPRODUCTION 55 



the higher, uni- cellular organisms are reached, there is a 

 gradual foreshadowing of organs ; and multiplication is 

 accompanied by a series of changes which are not quite 

 clearly understood. We have, for example, in Amoeba, 

 a mere fission, or, as in the Yeast plant, a type of bud- 

 ding, but in Paramcecium there is conjugation and an 

 exchange of nuclear material. Among the primitive 

 forms, it is worth noting that the conjugants are fre- 

 quently derived from the same parents. This is 

 exhibited in a marked degree in the sexual reproduction 

 of Eurotium and Ulothrix, and another example of this 

 self-fertilisation is seen in Vaucheria. From this indis- 

 tinct differentiation of the sexual elements we pass to 

 such forms as Mucor and Vorticella, where there is a 

 conjugation of cells which are never derived from the 

 same organisms. 



In examining the lower forms of living organisms we 

 see a growing tendency towards amphimixis, or the 

 sexual mode of reproduction, and we may conclude that 

 this sexual mode is important, when we consider the 

 marvellous means taken to bring it about, and the final 

 disappearance of all other modes in the higher plants 

 and animals. 



But even after the sexual method has been adopted, 

 there is often a continuation of the asexual which may 

 indeed be the chief method of reproduction, as is well 

 shown by such forms as Hydra among animals, and the 

 leek, the shallot, the daffodil, and the potato among 

 plants which are propagated by bulbs and tubers respec- 

 tively. Again, we may have a curious alternation of the 

 two methods, as, for example, in Obelia, where the 



