242 THE GERM-PLASM 



which muhipHes sexually do not contain precisely identical 

 determinants, but these differ more or less from one another, 

 at any rate to such an extent that they correspond to the 

 individual differences existing in the species at the present day. 

 It results from the mechanism for nuclear division \\\^X all the 

 different kijuis of ids pass into all the cells througJwiit ontogeny, 

 and therefore the character of every individual cell occurring in 

 ontogeny must be deter nmied by an aggregate of ids ; so that all, 

 or at any rate the greater portion of the ids of which the idants 

 are made Jip, determine the constitution of the cell in question, 

 this determination resulting from the forces luithin the cell. 

 These preliminary remarks will serve as a general basis for the 

 following considerations on the effects of sexual reproduction. 



We can now consider the process of the ' reducing divisions ' 

 somewhat more closely. We require to know ivhat influence the 

 ?' educing division exerts on the composition of the germ-plasm, 

 ajid of what kind are the ids which are consequently respectively 

 removed fro)u, and retaijied in, the ger?n-plasm. 



Direct observation of the process is not alone sufficient to 

 explain it ; for not only do the ids and idants appear alike to our 

 eyes, but we cannot even determine whether the idants of the 

 young germ-cells of a new individual are the same as those of 

 the fertilised egg-cell from which this organism arose ; that 

 is to say, whether an idant is 2l permanent structure, and whether 

 a particular idant remains the same from one generation to 

 another. 



We know that during the process of amphimixis the paternal 

 and maternal idants are situated close together, and are en- 

 closed within a common nuclear membrane. There is often a 

 small, though distinct space between the two groups of rods ; 

 and did this remain distinct during the whole period of ontog- 

 eny until new germ-cells were formed and underwent reducing 

 divisions, we might be able to determine directly whether the 

 paternal and maternal groups became separated, or whether half 

 the number of the paternal rods remained in connection with the 

 maternal ones, or also whether different combinations of rods 

 are removed by the reduction. 



The matter is, however, not so simple as this : the idants of 

 the fertilised ovum only retain this form during the first division 

 of the egg-cell, and then become broken up into a number of 

 minute granules, which are distributed throughout the nuclear 



