1904] BRIEFER ARTICLES 46 5 
other words, the spirem is double; and its double nature results, not 
from an early longitudinal split, but from the presence of two separate 
and distinct threads. 
The two threads are in general parallel; in many places they are 
loosely twisted about each other, in others they diverge more or less 
widely. Almost immediately after their complete formation they 
approach each other more closely, become appressed and twisted about 
each other, and finally fuse into a single thread whose appearance gives 
no evidence of its double origin. 
After the formation of the two threads and before their fusion, each 
one shows in favorable material (especially if stained with Heidenhain’s 
iron-alum-haematoxylin) a differentiation, noted by many writers, into 
darkly-staining chromatin bodies (chromomeres) and a more lightly- 
staining ground substance, or linin. As the threads approach each 
other, they become so arranged that in general, though with occasiona 
exceptions, each chromomere in one thread lies opposite one in the 
other thread; and the fusion of the threads is followed by a fusion of 
the chromomeres in pairs. The single thread formed by the fusion 
then contains a row of chromomeres which show no sign of their 
double origin; but each original chromomere, as well as each one 
resulting from the fusion, is plainly made up of a large number of 
smaller granules. 
This fusion of the threads and of the chromomeres occurs very 
early in the period of synapsis; but after the fusion the synaptic con- 
dition persists, certainly for days, perhaps for a week or more. Toward 
the end of this period, the aggregation of the spirem becomes gradu- 
ally looser, and there follows a stage in which the thread is very evenly 
distributed throughout the nuclear cavity, and is in contact with the 
nuclear membrane at very many points. 
While the spirem is in this distributed condition, it becomes longi- 
tudinally split, the splitting of the thread being preceded by a fission 
of each chromomere. The halves of the split thread are much twisted 
about each other, and, except for the manner of its distribution within 
the nucleus, the appearance of the spirem at this stage is in all respects 
strikingly similar to its appearance immediately before the original 
fusion. 
There now ensues another change in arrangement; the thread is 
drawn inward from many of its points of contact with the nuclear 
membrane, and the greater proportion of its mass becomes aggregated 
in the central portion of the nuclear cavity, giving rise to a figure 
