XII.] CONJUGATION AND SEXUAL REPRODUCTION, II7 



followed from this view that the ancestral units contained in the 

 spermatozoa must also have undergone a diminution by half. 

 I postulated therefore a reduction of the spermatozoa by divi- 

 sion, and, to my mind, there was 'no doubt' that this process 

 occurred in them 'at some time and by some means \' although 

 not perhaps in the same manner as in the ova. I even said from 

 the very first- that 'it is quite conceivable' that this division 

 might occur in a manner entirely different from that of the &gg, 

 since in the former case both daughter-cells might be of similar 

 size and might become spermatozoa, in which case neither of 

 them would shrink and become polar bodies. 



The Maturation of the Spermatozoon. 



I have not been able to make out, by my own investigations, 

 the facts which confirm the soundness of these views as to the 

 spermatozoa ; my impaired eyesight, which has so often put a 

 stop to microscopic investigations, has again rendered the con- 

 tinuation of this research impossible. But Oscar Hertwig ' has 

 recently given us an account of the development of the sperma- 

 tozoa of Ascaris megalocephala, which not only proves the 

 reduction of the male germ-cells by division, but also shows 

 that it takes place in precisely that way, which from the first I 

 had regarded as most likely. 



Since these new facts affect our conclusions with regard to 

 many aspects of the process of fertilization, they are here shortly 

 abstracted. They may possibly enable us to penetrate still 

 more deeply into the meaning and significance of the processes 

 by which the nuclei of germ-cells are reduced in size. 



Ever since Edouard van Beneden's classical researches on the 

 process of fertilization, it has been well known that Ascaris 

 megalocephala is one of the most favourable objects for the 

 observation of the minute arrangements and changes occurring 

 in the nuclei of germ-cells. The nuclear loops are not only 

 relatively very large, but are also very few in number. Boveri 

 was the first to show that, as regards this number, two varieties 

 of the species exist, one containing two nuclear loops in the 

 young germ-cells, the other containing four. O. Hertwig then 



1 Vol. I, p. 381. • 2 Vol. I. p. 385. 



^ O. Hertwig, ' Ueber Ei- und Samenbildung bei Nematoden/ Archiv f. 

 mikr. Anat. 1890. 



