352 The Spermatogenesis of Bufo Lentiginosus 
monly found in the cells of the preceding generations. In the very 
young spermatocyte the chromosomes are still distinct, and they appear 
as very short, thick rods which are connected by fine linen fibres (Fig. 
10). In a slightly older cell, (Fig. 11), the chromosomes are found to 
be irregular in shape while the linin fibres connecting them are somewhat 
coarser and stain more intensely than in the younger cell. As the 
spermatocyte increases in size, the chromosomes gradually disappear, 
their substance going to form the nuclear reticulum which is constantly 
growing in amount (Figs. 12-14). At the stage of Fig. 13, minute 
granules of chromatin are first found scattered along the linin threads. 
As the substance of the chromosomes becomes distributed throughout 
the nucleus, the reticulum appears to be composed of a single series of 
deeply staining, rounded granules which lie so close together that it is 
almost impossible to make out the linin threads (Fig. 14). 
At the end of the growth period of the primary spermatocyte (Fig. 
15), the nucleus has increased enormously in volume, and it is very 
large in proportion to the size of the cell. , At this time the chromatin is 
in the form of a granular, much convoluted spireme which is apparently 
continuous. The spireme always appears perfectly homogeneous and 
never shows any indications of a longitudinal splitting. 
In the nucleus of the spermatocyte shown in Fig. 11, many of the 
chromosomes are found to be connected by two parallel linin threads. 
Such a pairing of the connecting fibres is much more noticeable 1n the 
later stages shown in Figs. 12-14. Judging from these figures alone, 
one might be inclined to think that each chromosome becomes split 
longitudinally during the formation of the nuclear reticulum in the 
young spermatocyte, and that the chromatin substance is later distributed 
along the linin fibres so that the paired threads found at the stages of 
Figs. 13 14, 18, 19, represent sister portions of longitudinally split 
chromosomes. This theory might indeed be plausible were the threads 
of the spireme invariably arranged in pairs at these stages in the develop- 
ment of the spermatocytes; but such is not the case. Sometimes, as 
shown at the top of Fig. 12, two chromosomes are connected by three 
linin threads and very often only one fibre connects two chromosomes. 
The pairing of the chromatin threads is most pronounced at the stage 
of Fig. 14, and it is rarely found at all at the end of the growth stage 
when the nucleus contains an apparently continuous spireme (Fig. 15). 
I do not, therefore, ascribe any special meaning to the pairing of the 
chromatin threads in the growth stages of the spermatocytes. The 
spireme is so long and so much convoluted at this time that it would 
