The Nebenkern iu the spermatogenesis of Pulmonata — Helix and Arion. 435 



The most important result of this research consists in the proof 

 I have adduced for the conclusion that in the attraction sphere (Neben- 

 kern) of Pulmonata no structures exist in any way comparable to 

 chromosomes. The salient characters by which these are recognised: 

 constant number, equal distribution to the daughter cells, and longi- 

 tudinal division, are absent. The figures show that the number of 

 the constituent elements ("Stäbchen", "Archoplasmaschleifen", "baton- 

 nets") varies considerably and that the total of twelve, given by 

 Platner, is frequently exceeded. The distribution to the poles is 

 frequently a very unequal one, and the fact that large masses con- 

 sisting of several "Stäbchen" may pass together to one of the poles 

 in very strong evidence against an equal division, especially by means 

 of longitudinal division. The form of the elements is also against the 

 possibility of such a mode of multiplication and the figures which 

 simulate such a condition are seen on careful analysis to result from 

 the approximation of the optical sections of a much curved surface. 

 Such considerations militate strongly against the supposed high im- 

 portance of the constituent elements of the sphere (Nebenkern) as 

 such. The importance of the attractionsphere from a morphological 

 and cytomechanical standpoint cannot be decided till our knowledge 

 of its origin and participation in the formation of the spermatozoon 

 is more complete. On these points I have no observations to oifer. 



The intervention of a well-marked resting phase of the chromatic 



between the two ripening divisions renders futile attempts to decide 



the relations existing between the daughter elements of the first 



spermatocyte division and those forming the equatorial plate of 



the second. 

 > 



K Appendix. 



^ The recent paper of Lee ^ ) came into my hands too late to re- 

 ceive notice in the text. Although dealing in the main with different 

 points there are in it a number of statements and conclusions which 

 are, to say the least, rendered improbable by the observations de- 

 tailed above. 



As regards the spermatogonia Lee states that the number of 

 chromosomes entering into the equatorial plate is 48 arranged in pairs. 



1) Lee, A. B., Les cinèses spermatogénétiques chez l'Hélix pomatia, 

 in: La Cellule, V. 13, Fasc. 1, 



