298 THE GERM-PLASM 



several, and indeed many, ids in the germ-plasm of each indi- 

 vidual. We know that the personal characters of the grand- 

 parents, as well as those of the parents, may reappear in the 

 offspring, and we may therefore conclude that hereditary units 

 or ids derived from the grandparents must be present in the 

 germ-plasm of this offspring, and that it must therefore be com- 

 posed of more than two ids. 



A similar conclusion is arrived at on other grounds. If the 

 assumption of hereditary units in the form of ids is once made, 

 it follows as a matter of course that their number must be 

 doubled in each process of amphimixis ; and it becomes evident 

 that this number must have increased enormously, in arithmet- 

 ical progression, if the ' reducing division ' had not intervened 

 and reduced it to the half before each occurrence of amphimixis. 

 This 'reducing division' must have appeared at a certain stage 

 in the phylogeny of amphimixis. If it arose in the germ-cells 

 of the first animal which was produced sexually, — supposing 

 that the germ-plasm of each of the parents previously consisted 

 of only one id, — it would always have caused the removal of 

 the id of one parent from each germ-cell of the offspring, and 

 thus no grandchild could ever have inherited characters from 

 both grandparents. According to our theory of the presence of 

 a large number of ids, such a case would seldom occur, although 

 it is apparently not impossible. A further consequence, how- 

 ever, would be seen in an unusually great uniformity in the 

 structure of consecutive generations ; for if only two ids were 

 present, one of which was always removed in the next genera- 

 tion, the same individual ids would pass through a great num- 

 ber of generations, and the diversity of the individual, such as 

 occurs to so great an extent in the human race, would be ex- 

 tremely limited. It is, however, just this extraordinary individ- 

 ual diversity which seems to me to be due to the multiplicity 

 of the ids ; it could not have been produced by only two ids 

 taking part in the process of amphimixis. 



Finally, as soon as we have recognised, on theoretical grounds, 

 the existence of ids at all, the fact that a number of them exist 

 in the cell is supported by direct observation. For whether 

 they correspond to the 'chromosomes' of other writers, which 

 I speak of as idants, or to the ' microsomes,' of which the 

 chromosomes are composed, as I assume to be the case, a large 

 number of ids may always be observed to be present in the cell. 



