6o 



CELL-DIVISION 



2. Heterotypical Mitosis 



Under this name Flemming i^^l^ first described a peculiar modi- 

 fication of the division of the chromosomes that has since been shown 

 to be of very great importance in the early history of the germ-cells, 



Fig 26 -Heterotvpical mitosis in spermatocytes of the salamander. [Fl.F.MMING.] 

 A Prophase, chromosomes in the form of scattered rings, each of ^vhich ''eP'-esents two 

 daughter chrom;somes joined end to end. B. The rings ranged about the equator of the spindle 

 .n divilS- the swellings indicate the ends of the chromosomes. C. The same viewed from the 

 snmdle-pole ' S! Diagram (Hermann) showing the central spindle, asters and centrosomes, and 

 the contractile mantle-fibres attached to the rings (one of the latter dividing). 



thouo-h it is not confined to them. In this form the chromosomes 

 split "at an earlv period, but the halves remain united by their ends. 

 Each double chromosome then opens out to form a closed rmg 

 (Fi- 26) which by its mode of origin is shown to represent two 

 dair-hter-chromosomes. each forming half of tlie ring, united by 



