LIFE HISTORY OF PRORODON GRISEUS. 31 1 



micro-nuclei of cither conjugant rarely undergo division. In 

 most cases but two of the micro-nuclei divide, and occasionally 

 but one divides. Those that do not divide show a very dark 

 center at first, becoming fainter, taking up less and less stain and 

 finally disappear within the cytoplasm by absorption (Figs. 17, 

 19). The activities in the origin, formation and division of the 

 four chromosomes are quite distinct (Figs. 16-18). Fig. 17 

 shows two micro-nuclei in either conjugant in the process of 

 division. The others are disintegrating. Fig. 18 shows but a 

 single division in either conjugant. While in Fig. 19 there is one 

 in one conjugant and two in the other which are dividing. The 

 significance of this variation in the number of micro-nuclei in the 

 third division is still an open question for explanation. The 

 inactive micro-nuclei may persist indefinitely before their final 

 absorption takes place. The micro-nuclei of the third division 

 migrate toward the anterior end of either conjugant, where they 

 complete their division and form the pronuclei (Figs. 19-21). 

 The third division differs from the first and second maturation 

 divisions in that there is an elongated connecting fiber between 

 the two daughter nuclei. This connecting fiber is not entirely a 

 part of the spindle, but is due more to the drawing out of the 

 nuclear membrane before separation is complete (Figs. 19-21). 



PRONUCLEI AND THEIR FUSION. 



There is a slight difference of size in the pronuclei of either 

 conjugant. The smaller can be considered as the moving 

 pronucleus and the larger as the stationary pronucleus (Figs. 

 20-2 1 ) . The interchange of the pronuclei is shown in Figs. 20 and 

 21. The fusion of the pronuclei occurs near the anterior ends of 

 the conjugants (Figs. 22-23). In the formation of the conju- 

 gation nucleus (amphinucleus), the pronuclei at first are spherical 

 and vesicular (Fig. 22). But later become slightly elongated. 

 The sides of the nuclear membranes in contact may persist for 

 awhile and prevent the direct fusion of the chromatin, giving the 

 appearance of a double fusion nucleus (Fig. 23). 



CLEAVAGE AND FORMATION OF NEW NUCLEI. 

 The number of divisions of the conjugation nucleus varies in 

 different forms. It may divide once, twice, three or even four 



