222 



MONTGOMERY — A STUDY OF THE CHROMOSOMES 



this would be a union of a paternal with a maternal chromosome. Also in the HemipLcra, 

 whenever there are in the spermatogonia two chromosomes which arc distinguishable from 

 the others by their greater size, as in several species described in this paper — e.g., Protenor 

 belfragei — these two especially large ones always unite together in the synapsis to form 

 oik! bivalent one much larger than the other bivalent ones, and one ot the large ones does 

 not unite with a small one ; now it can be shown that one of these large chromosomes is 

 paternal and the other is maternal. For calling the two large chromosomes of the sper- 

 matogonia a and b, respectively, they unite in the synapsis to form the bivalent chromo- 

 some ah ; the first maturation mitosis (here ;i, redaction division) gives a to one daughter 

 cell (second spermatocyte) and b to the other; the second maturation division of the one 

 of these daughter cells gives to each spermatid hi, the corresponding division of the other 

 daughter cell ib to each spermatid. What we find in each of these spermatids is only 

 one especially large chromosome, and not two. Accordingly, in order for there to be two 

 in the spermatogonia, the egg cell must furnish one, and then that one, together with the 

 one furnished by the spermatozoon in fertilization, would make up the two. Then of the 

 twO particularly large chromosomes of the spermatogonium, one would be paternal and 

 one maternal, and since these two unite in tin; synapsis stage, this would be a union of a, 

 paternal chromosome with a maternal chromosome. A case where two particularly large 

 chromosomes arc distinguishable in the spermatogonia was selected for discussion, because 

 these two, on account of their peculiarity in size;, can be recognized through the matura- 

 tion divisions; but if the conclusion be true that one of the large chromosomes is paternal 

 and one maternal, and that these two join together in the synapsis, then it would be very 

 probable that each of the other bivalent chromosomes of the spermatocytes represents a, 

 univalent paternal chromosome united with a univalent maternal one. This ease, as the 

 one of Asearls megalocephala univalens, may be considered very positive cases in favor of 

 the union of paternal with maternal chromosomes in the synapsis stage. There is still 

 another point of view which makes this conclusion very probable. As we have seen, 

 whenever there is an even number of chromosomes in the spermatogonia, exactly half that 

 number of bivalent chromosomes are formed in the synapsis ; thus in EucMstm variolarius 

 there are fourteen univalent chromosomes in the spermatogonia, and seven bivalent ones 

 in the first spermatocytes. Now seven of these chromosomes are paternal and seven ma- 

 ternal, since the spermatids have only seven. The regular formation of seven bivalent 

 chromosomes in (Iks synapsis stage would he oidy possible if maternal chromosomes united 

 with paternal ones. For if, on the contrary, paternal chromosomes united with paternal 

 and maternal with maternal, then of the seven paternal chromosomes three bivalent ones 

 could be formed, but there would be left an ununited odd one, and similarly of the seven 

 maternal chromosomes there would remain an ununited (univalent) odd one. But since 



