112 BULLETIN 120, UNITED STATES NATIONAL MUSEUM. 



(fig. 78, c). Several daughter cells were seen with the two daugh- 

 ter nuclei pear-shaped and connected by a slender thread. It seems, 

 therefore, that fission is consummated when the two nuclei are 

 dumb-bell-shaped and much constricted. In figure 78, c is shown a 

 large individual ready for fission. Each of its nuclei seems quite 

 clearly to show four chromosomes in each end of the dumb-bell. 

 But I am puzzled by another individual with a single spindle- 

 shaped nucleus which lies tilted up at an angle of 45°. In this 

 nucleus there is a ring of what are apparently macrochromosomes 

 around the equator of the spindle, and their number seems quite 



a 



Fig. 78. — Zelleriella hylaxena, X 460 diameters : a and b, individuals of the ordi- 

 nary SCUT ; c, A A large cell ready for fission, the macrochromosomes on the 

 under side of its nuclei drawn only in outline. 



clearly to be six. It seems that this must be abnormal, for a uni- 

 nucleated individual should not, in this species, have a spindle- 

 shaped nucleus. It should have either a much constricted dumb- 

 bell nucleus, or, if older, two daughter nuclei either connected or 

 not by a thread. Because of this peculiar nucleus one hesitates to 

 say positively that there are four massive chromosomes in this | 

 species, yet apparently this is the number. 



Zelleriella hylaxena resembles some individuals of Z. patagonien- 

 sis. The posterior point is developed to about the same extent, but 

 the former species does not show any of the more wedge-shaped in- 

 dividuals such as are seen in Z. patagoniensis. The two species 

 might perhaps be confused were it not that Z. patagoniensis has 

 eight macrochromosomes while Z. hylaxena has apparently four, 

 certainly not eight. 



