REPRODUCTION AND HEUEDITY 319 



hybrids, therefore, do not possess a hybrid character, like the 

 egg-cell from which they developed, but the germ-cells that are 

 formed are pure, at any rate, with regard to the ' character-pair. 



It will already have been observed how fully this assumption 

 agrees with our observations concerning the origin of sex- 

 cells, for this separation o the paternal and maternal rudi- 

 ments takes, of course, place daring both ( maturing-divisions ' 

 through which all germ-cells have to pass in the course of 

 their development. Let us endeavour to make this clear with 

 an assumed case (compare figs. 72 and 74). 



Let us assume that the ripe germ-cells of Mirabilis Jalapa 

 contain only two chromosomes, and that one entire nuclear loop 

 is the carrier of the 'rudiments' (Anlagen) of the colour of the 

 flowers. Whether we think of the mother as red-flowering and 

 the father as white-flowering, or vice versa, is of no importance to 

 the course of the process. In our illustrations the nuclear loops 

 are indicated in the red-flowering parent by a little black, in the 

 white-flowering by a white circle. During the act of fertilization 

 these ' rudiments ' of both parents are united in the fertilized egg- 

 cell, and all body-cells of the hybrid have the same structure as the 

 ovum. But as in Mirabilis Jalapa both ' rudiments ' endeavour 

 in an equal manner to reach development, the hybrid which 

 develops from the egg-cell must take up a middle position 

 between its parents and produce pink flowers. If now these 

 hybrids proceed to the formation of germ-cells, the before- 

 mentioned reduction-process sets in, by which the complement 

 of chromosomes is reduced by half and the idioplasm inherited 

 from the mother and father separated. The result of this double 

 division is represented in fig. 74, G. Each original germ-cell has 

 produced four mature sex-cells of which two have received the 

 ' rudiments ' of the red, two those of the white colour. If we 

 now cross the hybrids there are manifestly four possibilities 

 in the union of germ-cells all having the same prospect of 

 realization (fig. 74, 7-10) : either ovum as well as sperm possess 

 only the ' red ' chromosome, or of the conjugating sex-cells one 

 is furnished with a ' red,' the other with a ' white rudiment ' this 

 case will naturally occur twice as often as the other or finally 

 there is the possibility that both germ-cells possess only the 

 white ' rudiment/ Corresponding to the different ' outfit ' of 



