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 Vahttc 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 rn 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 



