372 K. MASUI: 
spiremes can not be seen, but they appear in about half the original number 
and twice as thick as those of the leptotene stage. Judging from these facts 
it seems most probable that conjugation of the chromosomes probably takes 
place by parasynapsis. Moreover, it is striking evidence in support of the 
conception of parasynapsis that during the synaptic stage partial fusion of 
two spiremes, which are arranged in pairs, frequently occurs (Fig. 18). 
The bivalent chromosomes thus united during the synaptic stage are so 
placed in the equatorial plate of the first division that their long axis is at 
right angle to that of the spindle (Text-fig. 2). The division begins to occur 
at the end of the chromosomes where the spindle fibres attach, and soon 
become separated into their components (Text-fig. 2). The above facts show 
conclusively that the halves of the bivalent chromosomes arranged at the 
equator of the spindle represent the conjugated univalent chromosomes. 
Therefore the first division is a reducing division. 
X. Summary. 
1. The resting nucleus of the spermatogonium contains a large nucleolus 
and several small chromatin masses. 
2. In the metaphase plates of the spermatogonia all the chromosomes 
are divided at the same time. In this stage it was not possible to count 
the chromosomes accurately, but many symmetrical pairs of the same were 
easily distinguished. 
3. The resting nucleus of the primary spermatocyte contains a large 
chromatic nucleolus. 
4. The conjugation of the chromatin’ threads takes place by parasynapsis. 
5. The chromosome nucleolus presents itself throughout the synapsis and 
the growth stages. 
6. In the primary spermatocyte the idiozome is conspicuously present. 
7. The number of chromosomes in the first division is nineteen, namely : 
eighteen bivalent and one accessory. 
8. The first division is reducing and heterotypic. The accessory chromo- 
some now passes undivided to one pole, thus producing two groups of 
spermatocytes, one with and the other without the accessory chromosome. 
