194 Macfarlane—Current Problems 
not only to some extent limited for the particular cell, but are 
also different at different periods in the metamorphoses of the 
nucleus. It is the rule that the youngest nucleoli are homo- 
geneous, and that vacuoles first arise when they have increased 
in size. Their size and number vary at different phases in the 
development of the nucleolus. Very frequently a number of 
smaller ones appear, and then these subsequently fuse together 
and produce a larger one.’ The first statement in the above 
quotation I would endorse, but must dissent from the remain- 
der, as being opposed to all conditions in vegetable tissues that 
I have examined. A small endonucleolus is seen alike in 
living and stained nucleoli in average embryonic cells. With 
advancing age of the cell the size and number of endonucleoli 
increase. It must be conceded that when viewed within the 
dense substance of the nucleolus, the endonucleolus possesses 
a rather vacuolar aspect, and it is probably true that its func- 
tion is to store some special liquid for the nucleolus. We 
cannot as yet speak definitely as to its constitution, but I 
would suggest that it possibly plays a special part in furnish- 
ing to the nucleolar substance some ferment or compound 
which may be utilized during the division period. To treat 
such bodies as haphazard vacuoles filled with cell sap will not 
conduce to a better understanding of them. 
Asregards that most attractive of all cell elements the centro- 
some I do not consider that we have evidence on which to 
base a safe conclusion. Strasburger’s excellent review of the 
position in his recently published work leaves us largely in 
doubt, but shows that much painstaking study has still to be 
engaged in. 
(b) PuystotocicaL Cytotocy.—Though it would be impos- 
sible arbitrarily to separate the two, I venture to affirm that 
great though the problems of morphological cytology have 
been, these will be equaled, if not eclipsed, in the near future 
by problems of a more purely physiological kind, while these 
