210 A. B. MACALLUM. 
stance diffused from the nucleus of the ovum into the cell- 
body. Born observed that the nucleoli are always placed as 
closely as possible to the cell protoplasm, while the chromatin 
in the development of the nucleus and ovum becomes so finely 
divided in the karyoplasm that it is stainable with great diffi- 
culty, and it is as difficult to demonstrate optically, a condition 
which continues till the formation or deposition of the yolk- 
grains (Dotterkérner) commences. In later stages the per- 
sisting peripheral nucleoli lose their capacity for absorbing 
colouring matters. 
In support of these observations of Schultze and Born, I 
may but add that the iron in the cytoplasm of the ovum makes 
its appearance only after the solution of the peripheral nucleoli 
commences. The substance forming the peripheral nucleoli 
does not react with staining reagents as does the chromatin of 
the nuclear network, and especially with the indigo-carmine 
staining fluid of Shakespeare and Norris the resulting stains 
of each are different, the chromatin of the network being 
coloured red while the nucleoli are stained blue or green, the 
latter colour obtaining also in the yolk-spherules of such pre- 
parations. A further difference is noticeable in the effect that 
ammonium hydrogen sulphide exercises when applied to these 
structures for some time at an elevated temperature. In this 
case the iron of the peripheral nucleoli reacts more readily 
than that of the chromatin of the network, but less readily 
than that of the yolk-spherules, which in the ova of Necturus 
and Amblystoma give a green reaction in a few minutes 
with the reagent. It would appear as if the iron compound 
undergoes a change in its transference from the nucleus to the 
cytoplasm. 
The peripheral nucleoli appear to be formed at the nodal 
points of the chromatin network, if one may judge from pre- 
parations of which fig. 384 is an illustration; but there is a 
possibility that these represent a pathological condition, 
since they are not common in the ovary when, if they were 
normal, they should be present in larger numbers. I have, 
moreover, found that they were accompanied by examples of 
