106 E. R. Downiye, 
has no polar radiations. Yet the cells of the developing embryo 
do have such polar radiations. The nearest approach to such 
asters in any mitosis observed either of interstitial or ectoderm 
cells is an occasional extension of the spindle fibres through the 
centrosome to the cell walls. Since the linin mesh work has 
been found during the prophase to form the thread on which 
the chromomeres are suspended, and since the entire structure 
goes into the chromosomes, the fibres of the achromatic spindle 
cannot arise from it unless they are outgrowths of the chromo- 
somes. This is apparently their origin as already noted. They 
originate at the periphery of the chromosome, one for each chromo- 
some, as a thread which elongates to the centrosome or beyond 
it to the cell wall. In disappearing however, the fibre seems to 
dissolve first at the end attached to the chromosome and then 
progressively toward the centrosome As the anaphase of mitosis 
occurs the previously attached ends of the separating chromo- 
somes are connected by fibres. 
On these interzonal fibres appear the Zwischenkörper (Fig. 39). 
They seem to disappear by absorption. 
The nuclear wall. This disappears in division shortly 
after the polar segmentation of the spireme into the individual 
chromosomes. It reappears immediately after the complete fusion 
of the chromosomes in the daughter nuclei. 
The chromosomes. The marked difference in shape of 
the chromosomes in the spermatogonia inside of the spermary and 
those at its border or without it is a point of interest demanding 
an explanation. The difference may be supposed to be due either 
to altered physical conditions, difference in pressure perhaps, or to 
altered chemical constitution, produced by some substance existing 
in appreciable quantity in the spermary. The phenomenon is quite 
common in spermatogenesis as we frequently find the chromosomes 
in the spermatocytes assuming a spherical form, or at least departing 
widely from the somatic form of a V or a rod. It may be due to 
a greater plasticity of the chromatin during reduction phenomena. 
The chromomeres. Whether these are actual parts of the 
living cell or are merely coagulation phenomena, they form our best 
criteria for judging the relation of certain apparently unlike chromo- 
somes. To homologize the V-shaped chromosomes with four distinct 
chromomeres of Fig. 21 and the spherical daughter chromosomes of 
Fig. 37 with two chromomeres was at first not deemed possible. It 
