BIGELOW: NUCLEAR CYCLE OF GONIONEMUS MURBACHII. 339 



by cytoplasm, the result of this being, as in the mitoses already de- 

 scribed, a crowding or contraction of the chromatic structures (Fig. 115) 

 which makes it difficult to trace in detail the formation of the chromo- 

 somes from the chromatic strands. There is, as already stated, no trace 

 of the occurrence of chromomeres, as is the case in the spermatogonia 

 and primary spermatocytes, but here, as in the entoderm cells, the chro- 

 mosomes that appear in the metaphase are probably formed by a simple 

 contraction and condensation of the segments. The cell represented in 

 Figure 115 shows stages in this process, which as a rule does not take 

 place synchronously throughout the whole of the nucleus. The chromo- 

 somes are still connected with one another by limn strands, which, for a 

 brief period after the disappearance of the membrane, seem stouter and 

 stain more deeply than before (compare Fig. 114 with Fig. 115); but 

 they disappear shortly after, so that by the time the chromosomes come 

 to lie in the equatorial plate no trace of the achromatic strands is to be 

 seen. 



The metaphase of the oogonial mitosis so closely resembles that of 

 the spermatogonial as to be practically indistinguishable from it. The 

 chromosomes form a typical plate, and both spindle and centrosomes can 

 now be seen for the first time. The achromatic figure (Fig. 118) is ex- 

 ceedingly simple ; astral radiations are entirely lacking ; and it in every 

 way resembles those of both somatic cells and male germ cells. The 

 chromosomes, which in the metaphase are distinctly dumb-bell-shaped 

 and very small, lie with their long axes parallel to the plane of cell 

 division (Figs. 116—118), and are generally well separated, so that 

 it is rather easy to count them. Unfortunately, the apparent number 

 increases with the progress of the splitting, so that to estimate the typi- 

 cal number care must be taken to choose only the very earliest steps in 

 the metaphase. From the few of this stage which I have been able to 

 study I have no doubt that the number is the same as in somatic 

 cells, in all probability twenty-four. 



The splitting of the dumb-bell-shaped rods is longitudinal, and begins 

 at one end ; so that when viewed from the pole of the spindle they form 

 V-shaped figures (Fig. 116), which later become separated into daughter 

 chromosomes, each having the same constricted form. The daughter 

 pairs seldom lie directly one above the other, and it is therefore often 

 possible in polar views of the late metaphase to count nearly twice the 

 somatic number, as is shown in the cell represented in Figure 116, in 

 which thirty-six are visible. The form of the chromosomes seems here 

 to have no special significance ; at any rate, it is not connected with any 



