VI.] THEIR SIGNIFICANCE IN HEREDITY. 387 



others. Thus, van Beneden and JuHn ^ stated in 1884 that 

 direct and karyokinetic nuclear divisions alternate with each 

 other in the spermatogenesis of Ascaris megalocephala. Again, 

 Carnoy - distinctly states that the different cell-generations in 

 the same testis may not uncommonly exhibit considerable 

 differences as regards karyokinesis. ' This may go so far 

 that direct and indirect division may proceed simultaneously.' 

 Platner^ 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 ob- 

 served, the form of karyokinesis which I have previously 

 interpreted as a ' reducing division ' occurs in the sperm- 

 mother-cells — a karyokinesis in which the chromatin rods 

 either do not divide longitudinally, or else divide in this way 

 after they have left the equatorial plate and are proceeding 

 towards the poles. Carnoy does not himself attach any special 

 importance to these observations, for he only considers them 

 as proofs that the longitudinal splitting of the loops may occur 

 at various periods in different species — either at the equator, or 

 on the way towards the poles, or even at the poles themselves. 

 We cannot conclude from the author's statements whether this 

 form of nuclear division only occurs in a single cell-generation 

 during spermatogenesis, as it must do if it really represents 

 a 'reducing division.' Until this point is settled, we cannot 

 decide with certainty whether the described form of karyo- 

 kinesis is to be considered as the 'reducing division ' for which 

 we are seeking. Fresh investigations, undertaken from these 

 points of view, are necessary in order to settle the question. 

 It would be useless to seek further support for the theory b}'^ 



^ E. van Beneden and Julin, ' La Spermatogenese chez I'Ascaride 

 megalocephale.' Brussels, 1884. 



^ Carnoy, * La Cytodierese chez les Aithropodes.' 



^ Gustav Plainer, ' Die Karyokinese bei den Lepidopteren als Grund- 

 lage fiir eine Theohe der Zelltheilung.' Internation. Monatsschrift f. 

 Anatomic und Histologic, Bd. IIL Heft 10. Leipzig, 1886. 



C C 2 



