1917] Boeck: Mitosis in Giardia microti 23 



(f) The chromosomes are about 0.3/u, in length and narrower in 

 width, uniform in size and show little or no differentiation. 



4. The centrosomes divide after the formation of the eight chromo- 

 somes; a paradesmose is formed between the daughter centrosomes, 

 one of which migrates 180° and the other stays fixed at the position of 

 the parent centrosome. 



5. Dispersal of the chromosomes in the nucleus takes place, fol- 

 lowed by their pairing in an order which seems to be that of their 

 former splitting and constriction in the spireme strands. The upper- 

 most chromosome of one spireme strand fuses with its mate of the 

 sister spireme strand, etc. This is a pseudosynaptic phenomenon. 



6. The four chromatic masses thus formed come down on to the 

 spindle formed from the linin. 



7. Later the chromosomes of each mass all appear in an end-to- 

 end position before final separation in the metaphase. 



8. In the metaphase, what is apparently a transverse division of 

 the chromatic mass to form the equivalent and uniform chromosomes, 

 is in reality the end of a longitudinal splitting which commenced pre- 

 vious to or at the time of the metaphase. The original plane of fusion 

 becomes the plane of division in the metaphase. 



9. In the anaphase the four chromosomes migrating to either pole 

 in each nucleus fuse to form a chromatic mass near each pole of each 

 nucleus. 



10. Completion of the constriction of the nuclear membrane results 

 in four daughter nuclei in which reconstruction has taken place. 



11. The division of the axostyle prior to mitosis represents the cyto- 

 plasmic change of a previous mitosis. 



12. All changes in mitosis are closely correlated with structural 

 changes in the cytoplasm. 



13. The cysts may be grouped under three types: (a) "single indi- 

 vidual" cysts; (h) " binary fission " cysts; (c) "multinucleate" cysts; 

 no stages were found in the material studied which were indicative 

 of copulation on the part of the individuals and the fusion of their 

 nuclei, or of maturative phenomena. 



14. The organelles of the fibrillar system, together with the two 

 nuclei and their related structures, present a single unified and inte- 

 grated complex, which constitutes the neuromotor apparatus. 



Transmitted March 9, 1917. 



