300 THOS. H. MONTGOMERY, 



come approximated, so that the two chromosomes of such a pair 

 together form a figure V or U, the bend or angle of the U or V 

 marking the central ends of the chromosomes (Figs. 60, 61, 63, 

 Plate 19; Figs. 65—83, Plate 20); these central ends are directed 

 towards the central pole of the cell, which we have defined as the 

 pole where the pole of the achromatic spindle had previously been 

 situated ; while the distal ends of the chromosomes, or correspondingly 

 the opening of the U or V, are directed towards the distal pole of 

 the cell, which has been defined as that region where the Zwischen- 

 körper plate had been formed. The distal ends of the chromosomes 

 are placed close to the distal surface of the nuclear membrane; but 

 their central ends are usually removed by a clear space of nuclear 

 sap from the central pole of this membrane; from this arrangement 

 it follows that the chromosomes seem to be placed nearer one sur- 

 face of the nucleus, and that the distal. 



Now the central ends of the two univalent chromosomes which 

 together form the U or V are seen to be connected by a linin band, 

 except when this band lies outside of the plane of the section, or when 

 the chromatin granules at the central ends of the chromosomes are 

 in actual contact and so hide this band; to this structure will be 

 applied the name, central linin band (Figs. 63, 66, 73, 75; in 

 most of the other figures it is hidden by the chromatin). As will be 

 shown later, this band of linin persists through the synapsis, telo- 

 phase, and rest stage, also through the prophase of the 1st maturation 

 division, but becomes divided in the metakinesis of that division. This 

 central linin band is most probably a persisting portion of the linin 

 spirem of the spermatogonic mitosis; and it is by its agency as a 

 contracting structure, or along it as a path for movement, that two 

 univalent chromosomes become united into one bivalent chromosome. 

 Accordingly, in Peripafus the mode of reduction of the number of the 

 chromosomes is as follows: every two univalent chromosomes of the last 

 spermatogonic mitosis become united into pairs by the approximation 

 of their central ends, along the path of, or by the direct contraction 

 of, persisting portions of the original linin spirem, the central linin 

 bands. 



In my figures of the synapsis and telophase stages I have shown 

 in most cases for each nucleus only those chromosomes which could 

 be seen plainly in their entirety. Chromosomes seen very obliquely 

 were not drawn in (except in Fig. 69). But in lateral views of nuclei 

 in the synapsis and later stages only a few of the chromosomes can 



