ON THE SPERMATOGENESIS OF THE SILK-WORM. 
143 
arise from the achromatic thread substance of the nucleus ; (3) 
they arise both from the achromatic nuclear constituents and 
from the cytoplasm. O. Hertwig states in his celebrated text 
book “ Die Zelle und die Gewebe” that, “ Ich have früher den 
Standpunkt vertreten und nehme ihn auch jetzt noch ein, dass, 
abgesehen von den Polstrahlungen, die dem Protoplasmakörper 
der Zelle angehören, die verschiedenen Structurtheile der Kern¬ 
figur von den einzelnen Substanzen des ruhenden Kerns abstam- 
. men. Die stoffliche Grundlage für die Spindel und die später 
aus ihr hervorgehenden Verbindungsfäden suche ich in dem 
Liningerüst.” 
t 
In the sperm-mother-cells of Bombyx mori, it seems to be a 
clear fact that the central spindle is derived from the cytoplasm 
as will be seen in figs. 40, 41, 42, 43, 47, and 49. Of the polar 
parts of the achromatic spindle, I am strongly inclined to believe 
that they are derived from the nucleus, because at the time when 
the central spindle is formed in the cytoplasm (figs. 36, 41, 42 
and 43), both the centrosome and radial fibres are as yet not to 
be seen. When centrosomes appear at the two poles of the 
spindle, the radiating fibres come distinctly into view (fig. 49). 
Let us now consider the origin of centrosomes. After the dis¬ 
covery of this body by E. van Beheden in Ascaris megalocephala, 
Flemming (8), Guignard (10), Strasburger (34), Heidenhein (13) 
vom Rath (29) and others have shown that they are present in 
the cytoplasm also during -the resting stage of the nucleus. I 
have also found a distinct centrosome with a well developed ar- 
choplasm in the resting sperm-mother-cells of Panulirus japonicus 
(figs, 87, 88, 89 and 90), but in the sperm-mother-cells of Bombyx 
mori, I am unable to detect the centrosome in the resting stage. 
Watase (42) considers the centrosome as an aggregation o 
the cytomicrosomes, and states that “ for the centre of the aster 
is the point where the greatest number of cytoplasmic filaments 
meet with one another and the size of microsomes produced 
at such a place must be correspondingly large. In other 
words, the microsome produced in the centre of the aster is the 
centrosome 1 ^.” A. Brauer (3, 4) discovered the formation of 
1) Schneiders ' 1 s observation is little different from Watase's. He states that the 
attractions—spheres consist of a convolution of thin threads, and the radiated threads 
form the “ Polsonne.” 
