LIFE HISTORY OF PRORODON GRISEUS. 309 



contraction during fixation (Figs. 8, 16). The nuclear activities 

 during conjugation can best be followed in the encysted forms, or 

 better perhaps in those that have just escaped from the cysts and 

 become expanded, since they are freer from stained food vacuoles. 

 The single micro-nucleus in the resting stage is always situated 

 near the macro-nucleus, but never within it (Fig. 7). 



FIRST MATURATION DIVISION. 



The micro-nucleus at first stains as a homogeneous mass with 

 a dark center (Figs. 1,7). It soon enlarges, migrates towards 

 the anterior end and becomes vesicular with a central chromatin 

 mass of granules on a spireme, surrounded by a large clear area 

 (Figs. 8, 1 6). The chromatin becomes concentrated into eight 

 distinct staining bodies, which become elongated (Figs. 8, 9). 

 In the first maturation spindle fibers extend towards either pole 

 and the eight chromosomes divide transversely, giving rise to two 

 equal masses or daughter micro-nuclei (Figs. 10-12). Immedi- 

 ately after division the two micro-nuclei pass into the resting 

 stage (Fig. n). 



SECOND MATURATION DIVISION. 



The second maturation division is similar to that of the first. 

 Both micro-nuclei in either conjugant undergo division. The 

 micro-nuclei with their darker staining center become vesicular 

 (Figs, n, 12). The chromatin at first in an irregular spireme 

 becomes condensed into four double-staining bodies (Fig. 13), 

 which elongate in the form of four double rods. The reduction 

 of eight single rods to four indistinct double rods can be con- 

 sidered as the reduction stage. The four bivalent chromosomes 

 become arranged on the equatorial plate parallel to the long axis 

 of the spindle, and apparently divide transversely instead of 

 longitudinally, as indicated in Figs. 14 and 15. At the close of 

 the second .division as in the first the chromatin passes into the 

 resting or more vesicular condition before the next division 



(Fig. 16). 



THIRD DIVISION. 



The four micro-nuclei resulting from the second division are 

 about the same in size when first formed (Fig. 16). The four 



