GENERAL A NA TOMT. 



69 



'j,.ch 



mm 



y%i 



somes, while from tliese poles fi]io threads, the spindle-fibres, 

 run to the centre or equator of the 

 nncleus. These fibres are in many 

 cases certainly derived from the 

 achromatic nuclear reticulum, while 

 in others a greater or less 2)art in 

 their formation is taken by the 

 jirotoplasm. X debated point is the 

 relations of the fibres in the equa- 

 torial plane of the spindle. Do all % 

 the fibres extend from pole to pole ? 



Do all of them end in the eriuatorial Fig. si.— Spindle formation nnddivi- 

 . ^ . sion of the centrosomes in A>-<:ari» 



plane, so that the spindle consists of megalocepliala. (After Brauer.) c, 

 ^ ' i! r-i T centrosomes; c/j. cliromosomes. 



two cones of fibres separated at the 



equator ? Or, lastly, are fibres of both kinds present in the same 

 spindle ? It would api)ear that differences exist in these respects 

 in different objects. 



All of the chromatin of the nucleus lies in the equator, united 

 in the 'equatorial plate,' but by this must not be understood a 

 connected mass but a layer of separate bodies, the chromosomes, 

 for the chromatin of the nucleus divides early into particles which 

 are rarely sj^herical or rodlike, but usually have the shajie of 

 U-shaped loops. Tliese chromosomes are of equal size in the same 



<-X 



Fig. 2:J.— Cell division in the skin of Sutaiiuuidni iiHU'iilnxn. (After Rabl.) 



cell, and, what is of greater theoretical significance, their num)jer 

 is identical in all the cells of all the tissues of one and the same 

 species. 



