ö28 THOS. H. MONTGOMERY, 



towards the centrosomes ; these mantle fibres are genetically the distal 

 linin threads of the chromosomes, and these threads are from the first 

 attached to the distal ends of the chromosomes 



Thus the mantle fibres have at the start insertions on the distal 

 ends of the chromosomes, and apparently these points of insertion do 

 not become shifted at all, or only to a very slight degree. Each 

 bivalent chromosome (compare the description of the prophases) is 

 made up of two univalent chromosomes, the central ends of which are 

 closely bound together by a central band of linin ; from the distal end 

 of each univalent chromosome a mantle fibre passes to one of the 

 pairs of centrosomes. By the tension of the mantle fibres the chromo- 

 some takes such a position in the equatorial plate, that the distal 

 end of one univalent component becomes directed towards one pole 

 of the spindle, the distal end of the other univalent chromosome 

 towards the other pole; thereby the central band of linin joining the 

 central ends of the two univalent chromosomes comes to lie exactly 

 or approximately in the plane of the equator of the spindle (Figs. 179 

 — 182, 184 — 186). It is on account of this arrangement of the distal 

 ends of the mantle fibres on the distal ends of the chromosomes, that 

 in the metakiuesis of the 1st maturation division the central linin 

 threads become ruptured, and accordingly whole univalent chromo- 

 somes become separated. 



But this conclusion, as to the arrangement of the axes of the 

 bivalent chromosomes in the 1st maturation spindle, was not deduced 

 only from the axial relations of the points of attachment of the mantle 

 fibres upon them. If at the end of the prophases, but before the 

 nuclear membrane has vanished and before mantle fibres have appeared, 

 the chromosomes, which have attained their definitive form, be examined, 

 their composition out of univalent chromosomes can be readily seen, 

 and is corroborated by the formation of the chromosomes in the 

 synapsis stage; the most frequent type of these chromosomes is that 

 of a bent dumbbell, the transverse constriction of which marks the 

 point of union of the central ends of two univalent chromosomes. 

 Now this constriction, which before, as we have seen, was marked by 

 the central linin fibre, subsequently comes to lie exactly in the plane 

 of the equator. Accordingly, even had I been unable to make any 

 definite observations as to the mode of origin of the mantle fibres, we 

 could notwithstanding deduce with certainty that in the equatorial plate 

 each bivalent chromosome becomes so disposed, that one of its uni- 



