320 THOS. H. MONTGOMERY, 



151 — 153, 155, 157 — 160, Plate 21). This is the most prevalent type, 

 and the one which shows the greatest similarity to the type found in 

 the synapsis and telophase. In some cases the two univalent chromo- 

 somes lie in the same straight line (sub-type I); this is shown in 

 Fig. 151, and in the diagram 253, I, of Plate 25. Such a chromo- 

 some gradually shortens to the definitive form of a straight dumbbell 

 (Figs. 161, 167, 168, 173, 175—177, 179—182; Plate 25, diagram 253, 1), 

 the definitive form. More frequently the two univalent chromosomes 

 form together as U or V (sub-type II) (Figs. 135, 136, 139, 140, 147, 

 151), and gradually condense to the definitive form of a curved 

 dumbbell (Figs. 153, 155, 157, 159, 161, 167—169, 171 -- 174, 179— 

 181, 182, 192); the evolution of this sub-type is diagrammatized in 

 Fig. 253, II. The definitive form of a bent dumbbell is the one most 

 frequently found in the monaster stage; and to obtain true lateral 

 views of chromosomes in this stage on should consider only those 

 chromosomes at the periphery of the equator, for the ones nearer the 

 centre lie in such a way as not to show their angle of curvature since 

 this angle is peripherally directed. In a third sub-type the two uni- 

 valent chromosomes lie approximately parallel to one another (Figs. 140, 

 141, 144, 145, 148, 156, 158, 161) and gradually condense (Figs. 170, 

 171, 173, 176, 178) to the definitive form of two thick parallel rods 

 (Figs. 179, 182, 185, 186). The mode of evolution of this third sub- 

 type is shown in the diagram 253, III, of Plate 25. This sub-type 

 differs from the other two in that the space separating the two uni- 

 valent chromosomes is parallel to the long axes of the latter. In all 

 these forms of chromosomes the longitudinal spht is clearly marked 

 only at an early stage, and then gradually disappears, or at least 

 remains faintly marked at only one end (then usually the distal), or 

 more rarely at both ends of each univalent chromosome. 



2) Bivalent chromosomes in which the two univalent chromosomes 

 are irregularly bent around one another, so that the whole represents 

 the form of a double spiral or an X. In the former case the central 

 ends of the univalent chromosomes are rather closely connected 

 by the central linin band, while the distal ends are unconnected 

 (Figs. 139, 142, 143, 146, 165), and assume the definitive form of 

 two shortened rods parallel to or slightly bent around one another 

 (Figs. 170, 173, 178); this sub-type, represented also in diagram 254, 

 IV, Plate 25, might equally well be considered closely related to sub- 

 type II of type I. Between these chromosomes and the second sub- 

 type of the 2nd type, where the univalent chromosomes lie across one 



