30 Olivo. Mitotic (li Vision ofthe uuclci ol' t lie Cyanopliyceae. 



4. Centers ol' divisiun activity occnii- willi rhytlnuic rc^ulai- 

 ity in tlio rilamentous forms, a phenomenon already noted in 

 Spiro(/i/ra (p. 24). 



T). The division of tlie central hody is mitotic, since we can 

 lind in the chan^es whicli it nnderf2;o(^<=; the iisual ])henonu'na 

 wliicli accompany niitosis in tlic higher organi.sms (pp. 20— 24). 



G. The kinoplasniic, achromatic portion of the central body 

 constitutes a „s])indle", whicli has the shape of a flattened disc 

 in the narrow celled species; and in tlie longer celU^d forms, of 

 a broad-poled, somewhat cylindrical figure; or, in still others, 

 narrow-poled and s])indle-formed. The achromatin consists of 

 a central spindle, which is offen very densely fibrous, between 

 the dividing chromosomes; and a portion leading from tlie 

 chromosomes to the cross walls. \vhich corresponds to the mantle 

 tibers in position and apparently in function (pp. 19 — 20). 



Owing to the peculiar phine of location of the nuclear 

 iigui'e in Glococap.sa^ there is little appreciable development of an 

 achi'omatic spindle (p. 29). 



7. A spireme arrangement of the chromatin granules is also 

 evident in the preliminary nuclear changes. The „segmented 

 spireme" in Gloeocajhsa appears to consist of a simple, more or 

 less Spiral thread, having about 8 chromatin granules held by 

 the linin, and situated in the middle of the cell, with its long 

 axis corresponding to the long axis of the cell (p. 29). 



In the filamentous species, the spireme apparently consists 

 of a much convoluted thread, and it is further probable that it 

 also is made up of a definite number of distinct chromatin 

 granules, arranged along a linin thread (pp. 22, 31). 



8. Finally, the most necessary requirement of mitosis is 

 f ultilled in that a longitudinal lission of the chromosomes occurs. 

 This is plainly evident in the case of Gloeocapsa. in which the 

 simple spireme thread divides lengthwise, beginning at the two 

 ends and Splitting thence progressively to the middle of the 

 thread. It is higlily probable, further, that the Splitting of the 

 convoluted spireme of the filamentous species takes j^lace in 

 a somewhat similar manner, since the fission plane begins at 

 the edge of the disc-shaped figure and travols progressively in- 

 ward to the middle (pp. 22, 23, 31). 



9. The number of chromosomes in the cells of the same 

 species is constant. There are 8 chromosomes in GJoeocapsa 

 polydermatica and No.stoc cotmnune] IG in Oscillaforia tctiuis, in 

 an undet. sp. of OsriUnfona^ Calofhrix tJiennaUs, Phormiflhim sp.; 

 and probably 32 in Oscillatoria prrncep.s and 0. Froeldichia (p. 19). 



Each chromosome apparently corresponds to a single cliro- 

 matin granule of the spireme thread. Should this prove true, 

 tlien this presents the hitherto unrecorded phenomenon of 

 a chromosome which consists of a single chromomere. 



10. The division of the cell is usually accomplished by the 

 growing in of a ring-formed wall, which appears to grow inde- 

 pendently of and simultaneously with nuclear division (p. 24). 



