OF THE GERM CELLS OF METAZOA. 221 



somes are bivalent and eleven in number, so that each group cannot have the same num- 

 ber. Thus out of the cases examined by him, in twelve cases the chromosomes were in 

 groups of relatively equal number (relation of six to five) ; in two cases, one group had 

 four, the other group seven chromosomes ; in three cases, they were arranged in groups of 

 three and eight, respectively ; and in one case, in groups of two and nine, respectively. 

 Thus, though there may be at the period of the first maturation mitosis an arrangement 

 of the chromosomes into two groups, yet the variable discrepancy in the number of the 

 chromosomes composing the two groups shows that it is impossible that one group has only 

 paternal chromosomes and the others only maternal, for the reason that at the start (in 

 the fertilized egg) paternal and maternal chromosomes are equal in number. Accordingly, 

 Riickert has shown for Oyclops that the maternal and paternal chromosomes form separate 

 groups up to about the 32-cell stage, when the separateness of these groups gradually 

 disappears ; and his own descriptions and figures would show that at the time of the 

 first maturation mitosis there is no longer a paternal group of chromosomes separate from 

 a maternal group. There could also be mentioned the observations of other authors to 

 the effect that the paternal and maternal chromosomes compose separate groups in the 

 early cleavage cells, as especially the observations of my colleague, Prof. Conklin, on the 

 eggs of Crepidula. 



Accordingly, we have seen that in the earlier period of the germinal cycle, at the 

 time of fertilization and the immediately following generations, paternal and maternal 

 chromosomes remain separated from one another, and also that the individual chromo- 

 somes show a remarkable degree of independence as evinced by their vesicular phenomena 

 in the anaphases. In the later stages of the germinal cycle, on the contrary, paternal and 

 maternal chromosomes appear no longer to be arranged in separate groups, and the chro- 

 mosomes themselves are no longer vesicular in the anaphases. 



Now for the bearing of all this on the question of the significance of the synapsis 

 stage. At the commencement of the germinal cycle, the stage of conjugation of the germ 

 cells, the chromosomes are more distinct from one another than at any later stage ; this 

 distinctness gradually disappears as the cycle progresses, and at the time of the synapsis 

 stage the chromosomes actually join together to form half the normal number of (bivalent) 

 chromosomes. What chromosomes are these which unite to form pairs ? Does a paternal 

 chromosome unite with a paternal and a maternal with a maternal, or does a paternal chro- 

 mosome unite with a maternal one ? The following considerations show that the latter 

 view is probably the true one. 



First of all, in Ascaris megaloc&phala univalens there is the normal number of two 

 chromosomes ; as Brauer (1893 b) has demonstrated, one of these is paternal, the other 

 maternal in origin ; since these two unite to form one bivalent one in the synapsis stage, 



