148 



PROTOZOOLOGY 



moving along the left arm to its tip, and the other entering and pass- 

 ing down the stem to join the posterior band. According to Summers 

 (1935) a process similar to that of E. eurystomus occurs in Diophrys 

 appendiculata and Stylonychia pustulata; but in Aspidisca lynceus 

 (Fig. 55) a reorganization band appears first near the middle region 

 of the macronucleus (6), divides into two and each moves toward an 

 end, leaving between them a greater chromatinic content of the 

 reticulum (c-i). Summers suggested that "the reorganization bands 

 are local regions of karyolysis and resynthesis of macronuclear 

 materials with the possibility of an elimination of physically or 

 possibly chemically modified nonstaining substances into the cyto- 

 plasm." Weisz (1950a) finds that the nodes of the moniliform macro- 



Fig. 54. Macronuclear reorganization before division in Euplotes 

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

 of the macronucleus; b-d, later stages. 



nucleus of Stentor coeruleus contain different concentration of thymo- 

 nucleic acid which is correlated with morphogenetic activity of indi- 

 vidual nodes, and that fusion of ill-staining nodes results in a return 

 of strong affinity to methyl green. It appears, therefore, concentra- 

 tion of bandform or moniliform macronucleus prior to division may 

 serve to recover morphogenetic potential prior to division. 



In a small number of ciliates, the macronucleus is distributed as 

 small bodies throughout the cytoplasm. In Urostyla grandis, the 

 macronuclear material is lodged in 100 or more small bodies scat- 

 tered in the cytoplasm. Prior to fission, all macronuclear bodies fuse 

 with one another and form one macronucleus which then divides 

 three times into eight and the latter are evenly distributed between 

 the two daughter individuals, followed by divisions until the number 

 reaches 100 or more (Raabe, 1947). On the other hand, in Dileptus 



