The Nebenkern in the spermatogenesis of Pulmonata — Helix and Arion. 429 



SO boldly stated in the introduction it is not so satisfactory as could 

 be desired. Thus as to the origin of the Nebenkern from the remains 

 of the spindle we read (1. c. p. 240): "En présence de l'impossibilité 

 qu' il y a à établir par l' observation ce que devient le cone fusorial 

 à partir du moment où il est dérobé à notre regard par les chromo- 

 somes qui r enveloppent en se constituant en noyau fille, je n' ai que 

 la resource de prier le lecteur d'admettre avec moi pour un instant 

 que le Nebenkern n'est autre chose que le cone fusorial persistant, 

 et de voir en quels points les caractères de ces deux éléments cor- 

 respondent." This is far from absolute demonstration. The spindle 

 fibres which are measured and compared in the succeeding paragraph 

 with the Nebenkern-elements, are not these of the spermatogonium 

 but of the first spermatocyte mitosis; the very division in which the 

 Nebenkern is supposed to disappear. 



As regards the origin of the achromatic figure Lee opposes the 

 results of most modern work as well as those of Platner. The 

 spindle is merely the nucleus which has taken this shape and become 

 fibrillar. The Nebenkern takes no part in its formation. The polar 

 radiations of the amphiaster are formed around two polar funnels 

 ("entonnoirs polaires") which are extruded from the nucleus through 

 pores in its membrane and serve to fix the nucleus to the cell-wall 

 during mitosis. There are no centrosomes either in the Nebenkern, 

 at the apices of the polar funnels, or at the centres of the amphi- 

 aster. The summits or points of convergence of the fibrils of the 

 polar funnels are occupied by the pores in the nuclear membrane by 

 which their substance is continuous with the interior of the nucleus. 

 In the sequel facts will be detailed incompatible with these views. 



The results of the present investigation may be briefly summarised 

 as follows: The Nebenkern is the attractionsphere of the spermato- 

 cyte and contains the centrosomes. Its rodlets are optical sections 

 of the folded condensed outer layer ("Rindenschicht"), and the division 

 into two parts which takes place at the beginning of mitosis is a 

 mass-division. A resting stage intervenes between the two last divi- 

 sions of the spermatogenesis, so that Helix is an unfavorable object 

 for the purpose of solving the reduction problem. 



II. The Nebenkern of resting Cells. 



When a resting spermatocyte of the first order of Helix pomatia 

 is examined in the living condition, the nucleus is clear and trans- 

 parent, and at one side of it a group of highly refractive curved 



28* 



