SUMMARY AND CONCLUSION 457 



one half remained inactive, and was then either passed on 

 as inactive ' blastogenic ' germ-plasm, or else became divided 

 up in the course of ontogeny into groups, which were passed 

 separately to the same region, viz., that of the bud. 



In all cases in which the power of budding was permanently 

 retained by the species, the occurrence of this process of 

 doubling of the germ-plasm seems to have persisted through 

 the ontogenetic stages from an early period ; for we find that 

 the individuals arising by gemmation very frequently vary in- 

 dependently of one another, and often even to a great extent. 

 But independent variation from the germ onwards implies- 

 the existence of special determinants in the ' blastogenic ' 

 germ-plasm. Medusae could never have been, produced from 

 polypes by budding if independently variable determinants 

 of the buds had not been present in the germ of the fertilised 

 ovum. We therefore assume that tivo kinds of germ-plasm 

 exist in those species in which alternation of generations occurs, 

 both of which are present in the egg-cell as well as in the 

 bud, though only one of them is active at a time and controls 

 ontogeny, while the other remains inactive. The alternating 

 activity of these two germ-plasms causes the alternation of 

 generations. 



T\\^ formation of germ-cells is brought about by the occur- 

 rence of similar processes in the idioplasm to those which cause 

 gemmation. One part of the germ-plasm contained in the ferti- 

 lised egg-cell remains inactive and ' unalterable,' — that is, it does 

 not immediately become disintegrated into groups, but is passed 

 on in the form of accessory idioplasm to certain series of cells 

 in ontogeny, and thus reaches the parts in which germ-cells are 

 to be formed. Thus the whole of the parental germ-plasm, 

 with all its determinants, forms the foundation of the germ-cells 

 which will give rise to the next generation, and the extremely 

 accurate and detailed transmission of parental characters to the 

 offspring is thereby rendered comprehensible. 



In multicellular plants and animals, the germ-plasm becomes 

 more complex in consequence of sexual reproduction^ in which 

 process the ids of two different individuals, the parents, are 

 accumulated in the fertilised egg-cell every time amphimixis oc- 

 curs. This has caused the occurrence of the ' reducing division,' 

 which accompanies the formation of male and female germ-cells, 

 and results in the number of ids and idants being reduced to 



