194 Macfarlanc — Current Prohlcnis 



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. 



As regards 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) Physiological Cytglogv. — 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 



