ROBERTSON: THE CHROMOSOME COMPLEX. 289 



SYRBri.A ADMIRABILIS. 



it might be stated in this way: Each fiber does not attach 

 to one of the spermatogonia! chromosomes that previously 

 conjugated to form the bivalent chromosome but rather to 

 a half of each member of the pair. The pair the members 

 of which were united end to end becomes a pair split 

 longitudinally, and the result of the splitting is two pairs 

 instead of one pair. Each of the resulting halves or pairs 

 may still be considered a conjugated pair, because it is made 

 up of two distinct spermatogonia! elements, as the original 

 conjugated pair was. One of these halves goes to one pole 

 and the other to the opposite pole. The behavior of the chro- 

 mosomes in a first spermatocyte division, as far as the ordinary 

 chromosomes are concerned, is much like that of those in a 

 spermatogonia! division. In both kinds of cells the chromo- 

 somes are paired. The difference is that in the spermatocyte 

 the members of a pair during mitosis (as well as at other times) 

 cling together by their proximal ends (sometimes by the dis- 

 tal ends), while in the spermatogonium the members of a pair 

 remain separate. In both cases the division is longitudinal 

 and always begins at the inner or proximal end. The division 

 of the ordinary chromosomes in the first spermatocyte is there- 

 fore not a reduction or cross division, not a separation of the 

 members of a spermatogonia! pair, but a longitudinal, an equa- 

 tion division, by which each of the resulting daughter-cells re- 

 ceives a half of all the ordinary chromosome elements that 

 were present in the mother-cell. The accessory, of course, 

 which does not divide in this mitosis, is an exception and will 

 be taken up later. 



Lastly, mention must be made of the chromosomes which 

 Montgomery describes as "irregular V forms" and which he 

 designates by "K." He says that "Whereas ring-shaped chro- 

 mosomes are frequent in the preceding late prophases they 

 are only very exceptionally found in the equatorial plate, so 

 that probably by the pull of the mantle fibers upon them these 

 ring forms change into the form of the chromosomes lettered 

 K." Montgomery has evidently seen no polar views of the 

 first spermatocyte equatorial plate. Figures 30 and 33 of 

 plate XIX and series 1-25 of plates XXI and XXII show with- 

 out doubt the presence of these ring forms in the metaphase. 

 His chromosome K is merely a lateral or an oblique-lateral 

 view of a ring tetrad that has gone part way into mitosis, and 



2-Univ. Sci. Bull., Vol. IV. No. 13. 



