REPRODUCTION 



125 



the macronucleus of Nyctotherus ovalis probablj^ produce smaller 

 spherules in their alveoli. 



When the macronucleus is elongated as in Spirostomum, Stentor, 

 Euplotes, etc., the nucleus becomes condensed into a rounded form 

 prior to its division. When the macronuclear material is distrib- 

 uted throughout the cytoplasm as numerous grains as in Dileptus 

 anser (Fig. 239, c), ''each granule divides where it happens to be 

 and with the majority of granules both halves remain in one daugh- 

 ter cell after division" (Calkins). Hayes noticed a similar division, 

 but at the time of simultaneous division prior to cell division, each 

 macronucleus becomes elongated and breaks into several small 

 nuclei. 



During the "shortening period" of the elongated macronuclei 

 prior to division, there appear 1-3 characteristic zones which have 



Macronuclear reorganization before division in Euplotes 

 X240 (Turner), a, reorganization band appearing at a tip 



of the macronucleus; b-d, later stages. 



been called by various names, such as nuclear clefts, reconstruction 

 bands, reorganization bands, etc. In Euplotes patella (E. eurystomus) , 

 Turner (1930) observed prior to division of the macronucleus a re- 

 organization band consisting of a faintly staining zone ("recon- 

 struction plane") and a deeply staining zone ("solution plane"), ap- 

 pears at each end of the nucleus (Fig. 53, a) and as each moves to- 

 ward the center, a more chromatinic area is left behind (b-d). The 

 two bands finally meet in the center and the nucleus assumes an 

 ovoid form. This is followed by a simple division into two. In the 

 T-shaped macronucleus of E. woodruffi, according to Pierson (1943), 

 a reorganization band appears first in the right arm and the posterior 

 tip of the stem of the nucleus. When the anterior band reaches the 

 junction of the arm and stem, it splits into two, one part moving 

 along the left arm to its tip, and the other entering and passing down 



