307 
Chromosomes in Living Organisms. 
must produce a resultant effect which would be a mean 
between the individual variations of the successive generations. 
If, however, in consequence of the repeated union of indi- 
viduals presenting a similar variation, the number of ids 
representing this variation be increased, the variation must 
become permanent. 
At each longitudinal splitting of the chromosomes during 
nuclear division, all the ids are halved and are equally dis- 
tributed to the succeeding generations of nuclei. The number 
of the ids would, however, become doubled at each sexual 
act, were it not for the reduction which takes place at the 
initiation of each sexual generation. Since this reduction is 
not due either to extrusion or to an absorption of the chro- 
mosomes, at least in plants, the only remaining explanation 
is that it is due to the fusion in pairs of the ids and therefore 
also of the chromosomes. In the processes of differentiation 
which take place in the nucleus of a spore-mother-cell during 
the prophase, the substance of each pair of ids aggregates 
into a single id. In this way the idioplasm of many and 
different ancestors enters into the formation of each indi- 
vidual id. I do not, however, consider that these ancestral 
plasms exist isolated in the id ; I regard them as completely 
fused into one. The number of the ids is doubtless, like that 
of the chromosomes, hereditarily determined : but the num- 
bers in different organisms certainly do not stand in any 
definite relation to each other, for even closely allied species 
of plants, which have ids of apparently the same size, some- 
times present different numbers of chromosomes : for instance, 
in the Liliaceae the nuclei of the spore-mother-cells contain, 
according to the species, 8, 12, 16, or 24 chromosomes. It 
would appear, therefore, that the number of the chromosomes 
possesses no deep significance : and do not the two externally 
indistinguishable varieties of Ascaris megalocephala , which 
have been so fully investigated, differ in that the nuclei of 
the one contain only half as many chromosomes as do those 
of the other ? 
It is now known, and the point has been made especially 
