ON THE SPERMATOGENESIS OF THE SILK-WORM. I43 



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 friiher den 

 Standpunkt vertreten und nehme ihn auch jetzt noch ein, dass, 

 abgesehen von den Polstrahlungen, die dem Protoplasmakdi per 

 der Zelle angehoren, die verschiedenen Structurtheile der Kern- 

 figur von den einzelnen Substanzen des ruhenden Kerns abstam- 

 men. Die stoffliche Grundlage fur die Spindel und die spater 

 aus ihr hervorgehenden Verbindungsfaden suche ich in dem 

 Liningeriist." 



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 Beneden in Ascaris megalocephala, 

 Flemming (8), Guignard (10), Strasburgcr (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'V A. Brauer (3, 4) discovered the formation of 



1) Schneiders'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." 



