428 J. A. MURRAY, 



up the Nebeukern is constant and equal to half the chromosome 

 number. When the centrosomes begin to move apart, the Nebenkern 

 segments are arranged in two groups, each group containing half of 

 the total number. On this follows a longitudinal splitting of each 

 segment by which process the number of segments around each centro- 

 some is again raised to the original number. It is important to note 

 in this account, that the splitting takes place after the separation 

 into two groups, not before, as would be necessary to make a com- 

 plete analogy with the division of the chromosomes during mitosis with 

 which it has been compared. The centrosomes move to opposite poles 

 of the nucleus each accompanied by its rosette of Nebenkern seg- 

 ments, and these constitute the principal rays or "Hauptstrahlen". 

 These remain unaltered during the metaphase, but again become 

 arranged in two groups as soon as the division of the protoplasm 

 and rounding ofi of the daughter cells is completed. In this way the 

 second ripening division is initiated without intervention of a rest- 

 ing phase. 



Zimmermann ^) recognised the division of the Nebenkern into 

 two parts at the commencement of mitosis, and although unable to 

 demonstrate the centrosomes, observed that the radiations were centred 

 around a point a short distance from the nuclear membrane. He ap- 

 parently did not distinguish the second spermatocyte division (second 

 ripening division). 



Lee ^) combats on almost every point the statements of Platner. 

 According to him the Nebenkern is the degenerating vestige of the 

 polar portion of the spindle and is absorbed by the cytoplasm in situ 

 when the spermatocyte enters on its next mitosis (1. c. p. 228): "La 

 portion polaire du fuseau subit, après chaque cinèse une dégénére- 

 scence pâteuse granuleuse qui aboutit à la formation du corps connue 

 sous le nom de Nebenkern; que cette dégénérescence est totale et 

 aboutit à l'incorporation dans le cytoplasme de tous les éléments de 

 la portion polaire du fuseau, et enfin qu' aucun élément du Neben- 

 kern n' intrevient à titre d'élément figuré et actif dans une cinèse 

 subséquente." 



It is true when one seeks for the evidence for the conclusions 



1) ZiMMEEMANN, K. W., Ueber den Kerntheilungsmodus bei der 

 Spermatogenese von Helix pomatia, in: Verh. Anat. Ges. 1891. 



2) Lee, A. B., Sur le Nebenkern et sur la formation du fuseau etc., 

 in: La Cellule, V. 11, Tasc. 2. 



