OP THE GERM CELLS OF METAZOA. 223 



in the first spermatocytes of Euchistus all the chromosomes are united into pairs, so that 

 there are no chromosomes remaining univalent, it follows that in this case it is impossible 

 that only chromosomes of like parentage should unite together. 



These considerations render it very probable that in the synapsis stage is effected a 

 union of paternal with maternal chromosomes, so that each bivalent chromosome would 

 consist of one univalent paternal chromosome and one univalent maternal chromosome. 

 This conclusion allows us to consider the synapsis stage in an entirely new light, and gives 

 an important significance to this stage. The synapsis stage then, which is characterized 

 by the union of chromosomes into bivalent pairs, may be considered the stage of the con- 

 jugation of the chromosomes. When the spermatozoon conjugates with the ovum there is 

 a mixture of cytoplasm with cytoplasm, of karyolymph with karyolymph, possibly also 

 an intermixture of other substances ; but there is then no intermixture of chromatin, for 

 the chromosomes then, as we have seen, remain more separated from one another than at 

 any other stage in fact, the paternal chromosomes seem to show a repulsion for the 

 maternal, inasmuch as they are arranged in two separate groups. But after this begin- 

 ning stage of the germinal cycle, the repulsion of the paternal for the maternal chromo- 

 somes gradually diminishes, is generally no longer recognizable in the last of the spermato- 

 gonic and ovogonic divisions, and in the synapsis stage instead of a repulsion we find a posi- 

 tive attraction between the paternal and maternal chromosomes. The reason for the final 

 union of these chromosomes is obvious : it is evidently to produce a rejuvenation of the 

 chromosomes. From this standpoint the conjugation of the chromosomes in the synapsis 

 stage may considered the final step in the process of conjugation of the germ cells. It is 

 a process that effects the rejuvenation of the chromosomes ; such rejuvenation could not 

 be produced unless chromosomes of different parentage joined together, and there would 

 be no apparent reason for chromosomes of like parentage to unite. At the same time the 

 so-called " reduction in the number " of the chromosomes is effected, but this is probably 

 not primal but rather a necessary result of the conjugation of the chromosomes. And 

 here the point may be made that really there takes place no reduction in the number of 

 the chromosomes in the germinal cycle, but " reduction in number " is simply a conveni- 

 ent phrase for expressing that in the synapsis the chromosomes unite to form pairs ; no 

 chromosomes have been lost, there is in the strict sense no .reduction in number. 



So we find that the synapsis stage has a very broad and important significance, of all 

 the stages in the germinal cycle second only to the initial stage of conjugation of the germ 

 cells. In the synapsis stage we see the final process in the conjugation of the germ cells, 

 namely, the conjugation of the chromosomes. Now following immediately upon the syn- 

 apsis stage comes the growth period of the spermatocytes and ovocytes that period when 

 the germ cells attain volumes greater than at any other period in the germinal cycle. 



