590 CHRISTIAN CHAMPY AND H. M. CARLETON 
of nuclear shape, we have also attempted to analyse, when 
possible, the factors responsible for this. 
In the present stage of cytology the interpretation of cell- 
function is largely based on purely descriptive methods. There- 
fore such reasons as we have been able to put forward in explana- 
tion of the diversity of nuclear shape are to be regarded more 
as reasonable suppositions than as proven statements. We 
are of opinion that it is better to run the risk of assigning false 
causes to the phenomena which we have observed, than to 
explain nothing by confining ourselves to purely morphological 
considerations. 
Only when cytology has acquired experimental methods will 
it be possible rigorously to determine the factors responsible 
for nuclear form and function. 
Although the details of the structure of the nucleus—and 
particularly those concerning the disposition of the chromatin 
and the alleged ‘ linin’ network—are controversial, observa- 
tions on nuclear shape are easily verified. For not only are 
the appearances similar with widely different methods of 
fixation and staining, but they can be controlled by observa- 
tions on living material. And, finally, corroborative evidence 
can sometimes be obtained by experimental methods such as 
tissue culture. 
2. Tuer RELATION BETWEEN NUCLEAR SHAPE AND 
SuRFACE TENSION. 
A spherical nucleus is found in hepatic and most 
other gland-cells, also in many nerve-cells and spermatocytes. 
Its shape may often be attributed to surface tension, being 
the result of a relatively fluid (nuclear) mass that is immiscible 
in the surrounding cytoplasm. Such nuclei are relatively 
rare in the animal body, for the spheroidal condition is not 
uncommonly associated with mechanical factors, e.g. furrows 
or canaliculi in the nuclear membrane. Such structures, 
which occur more often than is generally supposed, sometimes 
make it difficult to say whether a spherical nucleus is the result 
of surface tension alone or of accompanying mechanical causes. 
