THE OVUM OF THE NINE-BANDED ARMADILLO. 121 



very clearly tetrads and others that are clearly bivalent though 

 not as yet tetrapartite. The small peripheral chromosomes of 

 earlier stages are still in evidence. Some of these show no 

 tendency to take a position in the spindle and are evidently 

 destined as a contribution of the nucleus to the cytoplasm on the 

 dissolution of the nuclear membrane. That this extrusion of 

 chromatin into the cytoplasm actually occurs is evidenced by 

 the presence in the cytoplasm of mature ova of minute nucleus- 

 like bodies of cytoplasmic chromatin. 



The spindle is evidently completely established within the 

 nuclear membrane as one must conclude from the occasional 

 occurrence of such appearances as that shown in Fig. 29. In 

 this case the membrane is exceedingly delicate but still un- 

 mistakable. When the membrane finally disappears there is 

 evidently cast out into the cytoplasm a large amount of material, 

 largely fluid, but probably partially solid in character. With the 

 loss of this liquid the spindle shrinks in size and the chromosomes 

 undergo marked condensation, as must be evident from com- 

 parison of these elements in Figs. 29 and 30 which are drawn to the 

 same scale. Still further condensation of chiomatin seems to 

 occur during the metaphase as a comparison of Fig. 34 will show. 

 The late prophases show the chromosomes as bivalent elements, 

 occasionally having the appearance of typical tetrads (Figc. 31 

 and 32). The spindle is apparently a naked central spindle 

 without mantle fibers or asters and is evidently a self-contained 

 system insulated from the cytoplasm by a sheath of inert material, 

 coarsely vacuolated, a material which may consist largely of the 

 extruded nuclear sap which is in equilibrium with the surrounding 

 cytoplasm, and through which no metabolic exchanges between 

 nucleus and cytoplasm can occur. 1 



In equatorial plate views of the metaphase one can frequently 

 count the chromosomes with every assurance of accuracy. Fig. 

 32 is a typical equatorial plate view of the first maturation spindle 

 and one can judge from this example as to the feasibility of enumer- 

 ating the chromosomes. By far the most frequent count obtained 

 is that of 16 diploid elements, but some counts show as few as 14 



1 These conditions accord with those described by F. R. Lillie for certain phases 

 of maturation in the egg of Nereis. 



