ON THE SPERMATOGENESIS OF THE SILK-WORM. 145 



konnen nicht von Pol zu Pol ziehen, sondern werden in der Nahe 

 des Spindelaquators durch ihren Ansatz an die sich farbenden 

 Kernbestandtheile eine Unterbrecbnung erleiden miissen." 



The " Nebenkern " is according to la Vallette derived from 

 cytomicrosomes, where he says (35) " hier wie dort ganz 

 unzweifelhaft seine Entstehung aus dem kornigen Zellplasma zu 

 constatieren," while Plainer (26) assigns its origin to the nu- 

 cleus. On this point he says: " Hier entwickelt sich aus dem 

 Kern ein eigenthiimliches, an frischen Preparaten glanzendes, 

 durch dunkleres Aussehen und homogene Beschaffenheit von 

 dem umgebenden Protoplasma sich unterscheidendes Element. 

 Es ist der Nebenkern in seiner ersten Anlage." Beside this 

 he (27) describes in the cytoplasm of the spermatocytes of 

 Lepidoptera, a structure which he designates by the name of 

 " Verbindungsbrucken." 



In the sperm-mother-cells of the silk-worm, we also find a 

 body which has the same appearance as both Platner % " Verbin- 

 dungsbrucken " and his centrosome. As it is present in the 

 cytoplasm even after the appearance of two centrosomes, it is 

 not a centrosome, so I will call it the "Verbindungsbrucken" 

 after Platner, although this body is sometimes found within the 

 cell and not always between the two neighbouring cells. It is a 

 round body surrounded by a free plasm and staining very deeply 

 by methylen-blue or Bohmer's hsematoxylin. There is generally 

 only one but sometimes two. Rarely it has a constriction form- 

 ing a dumb-bell-shaped rod. When it is present in the cyto- 

 plasm, it corresponds very well with the centrosome of Platner 

 (25) who observed it in many Lepidoptera (cf. his figs. 3, 4, 

 5). After the complete formation of the spindle, it dissolves 

 and is no more to be seen. Up to the present the function of 

 this body is quite obscure and requires further investigations. 



Besides the " Verbindungsbrucken " we observe in the 

 cytoplasm an aggregated spot of microsomes which afterwards 

 changes into the central spindle. It resembles very much in 

 shape the " Nebenkern " of la Valette (35, 36) and originates also 

 from the cytomicrosomes. Hermann (17), Solger (32), Platner 

 (25) Ishikawa (22) and others consider the "Nebenkern" to be 

 a centrosome with archoplasm. This seems to be the case in 

 Panulirus japonicus referred to above. But the structure known 



