1 4 C. IBHIKAWA. 



;ibs<eiice or pi'esence of iiuoleoli, :is stated ahovc, and tliis T lliiuk we 

 shall be able to explain hy tlie difference in growth between the two 

 kinds of cells. 



c. Tlu Zone of Wpeuiug. — This is the most important zone for 

 us, because we find here in l)<)tli egg- and spermatic-cells a kind (^.f 

 cell-division that we find nowhere else. This is the occnrrence of 

 tivct successive nuclear dirisinns witliouf <ni inteyrcniiuj restiuij sinije ami 

 the reiluction into li alt of the miinher of chroinoso}nes in the seeond of these 

 divisions. 



As observed first liy Plainer,^'^^^ so for as my knowledge goes, 

 and recently to a mncli greater extent by Hertivig^^^^ in Ascaris 

 inegalocephala, there occurs no case of such a division exce])t in the 

 U'enital cells, so that these processes cjin rightly be looked upon as 

 corresponding stages of tl\e egg- and spermatic -cells ( l^hitner, Hertwig). 



'Ilie nuclei that haA^e been resting for some time in the last stage 

 beoin to be active in this stao-e. Tlie chromosomes gradually come 

 int(^ yiew and liegin to arrange themselves in a circle under the 

 infliiencc (?) of the attractive centres which also now appear. The 

 number of chromosomes I counted to lie eight. In the sjiermatic cells 

 we can follow the steps from their dissolution and their gra.dual 

 shortening till the formation of dumb-bell shaped figures. Ihit in the 

 case of eggs the first distinct appearance of the chromosomes sliows 

 them already to be in that form. The division of these pi'oduces two 

 cells of ecpinl size in the case of the male elements, while in that of 

 the female one of the resulting cells is much larger than the other, and 

 thus are produced the egg and the first polar body. In all cases, how- 

 ever, the resulting cells contain each eight single chromosomes. The 

 nuclei of these cells do not, as said before, go through tlie resting stage 

 usual with a karyokinetic cell-division, but hegin to divide iunnrdiatehj 

 and produce incase of speruiaiic cells fuur cells eacli with four chromatic 



