THEIR SIGNIFICANCE IN HEREDITY. 375 



of development ; but we do not at present know of any such causes. 

 I should not consider the influence of the specific histogenetic 

 nucleoplasm, i.e. the spermafcogenetic nucleoplasm, to be such a 

 cause, because the quantitative proportions are very different from 

 those which obtain in the formation of egg-cells, and because it is 

 not inconceivable that the small quantity of true germ-plasm 

 which must be present in the nuclei of the sperm-cells at every 

 stage in their formation might enter upon a 'reducing division' 

 with 4 the spermatogenetic nucleoplasm, even when the latter pre- 

 ponderated. 



As soon as we can recognize with certainty the forms of nuclear 

 division which are 'reducing divisions,' the question will be settled 

 as far as spermatogenesis is concerned. It has been already estab- 

 lished that various forms of nuclear division occur at different 

 periods of spermatogenesis. I make this assertion, not only from 

 my own observations, but also from observations which have been 

 made and insisted upon by others. Thus, van Beneden and Julin 1 

 stated in 1884 that direct and karyokinetic nuclear divisions 

 alternate with each other in the spermatogenesis of Ascaris megalo- 

 cephala. Again, Carnoy 2 distinctly states that the different cell- 

 generations in the same testis may not uncommonly exhibit con- 

 siderable differences as regards karyokinesis. ' This may go so far 

 that direct and indirect division may proceed simultaneously.' 

 Platner 3 , in his excellent paper on karyokinesis in Lepidoptera, 

 also points out that the karyokinesis of the spermatocytes is 

 essentially different from that of the spermatogonia. According 

 to his description, the latter form may be very well interpreted as 

 a ' reducing division,' for no equatorial plate is formed, and the 

 chromatin rods (or granules, as they are better called in this case) 

 remain from the first on both sides of the equatorial plane, and 

 finally unite at the opposite poles to form the two daughter-nuclei. 

 Furthermore, if Carnoy has correctly observed, the form of karyo- 

 kinesis which I have previously interpreted as a ' reducing division ' 

 occurs in the sperm-mother-cells a karyokinesis in which the 



1 E. van Beneden and Julin, ' La Spermatoge'nese chez 1'Ascaride me'galoce'pliale.' 

 Brussels, 1884. 



2 Carnoy, ' La Cytodie'rese chez les Arthropodes.' 



3 Gustav Platner, ' Die Karyokinese bei den Lepidopteren als Grundlage fur eine 

 Theorie der Zelltheilung.' Internation. Monatsschrift f. Anatomie und Histologie, 

 Bd. III. Heft 10. Leipzig, 1886. 



