134 0N THE SPERMATOGENESIS OF THE SILK-WORM. 
two nucleoli are found in the nucleus of this stage, these 
gradually migrate towards the periphery of the nucleus facing the 
centre of the cyste (rarely, facing the wall of the cyste) and are 
finally pushed out into the cytoplasm one after the other through 
the nuclear wall at this point (figs. 33*38, c, d ). Placed in the 
cytoplasm the nucleoli seem to change their quality, since they 
now stain differently from what they did when they were in the 
nucleus. This is shown by the use of Hermann’s triple stain¬ 
ing, by which the nucleolus in the cytoplasm takes a brownish 
colour, while it colours deep red so long as it is within the nucleus. 
The further fate of the nucleoli in the cytoplasm is not known. 
After the disappearance of the nucleoli from the nucleus, 
two attraction-spheres make their appearance in the cytoplasm 
just at the same place where they disappeared. These two 
attraction-spheres gradually recede from one another until they 
come to the opposite poles of the nucleus. Some faint achro¬ 
matic fibres are seen running between these two attraction- 
spheres at this time (fig. 48). 
Before the extrusion of the two nucleoli from the nucleus, 
we can distinctly see in the cytoplasm between the nucleus and 
the wall of the cyste, an aggregation of microsomes (fig. 40), 
which in all appearance are like the “Nebenkern” described by 
la Valette St. George in a testis of Forficula auricularis (36) and 
others. This aggregation of cytomicrosomes has not always the 
same appearance in the sexual cells of the same cyste, and some 
of them present fibrous structures very similar to those of the 
achromatic spindle (figs. 36, 41-43, 47). As shown in figs. 36 and 
41 this fibrous bundle is seen at first parallel to the base of a cell. 
As Henking (15, 16) and others have already shown in other 
animals, all the genital cells of Bombyx mori m the same cyste 
are nearly in the same stage of development. Consequently 
we may say that the aggregation of cytomicrosomes found in 
one cell and the fibrous bundle in the other are two successive 
stages, the former changing into the latter. 
The fibrous bundle, above mentioned, takes somewhat oblique 
position and gradually approaches the nucleus, and, when the at¬ 
traction-spheres come to lie in the opposite sides of the nucleus, 
it connects with them forming a spindle (figs. 42, 43, 47, 49). 
The fibrous bundle, or the spindle, thus formed (fig. 49) consists 
