SHAPE OF THE NUCLEUS 607 
between nucleus and cytoplasm, nuclear polymorphism may 
result. 
(2) Mechanical deformation of the nucleus is com- 
mon and may be due to various causes, chief amongst which 
are: (a) Pressure from cytoplasmic inclusions, 
e.g. fat, lecithin, and yolk; (b) Tonofibrillae; (c) in 
striated muscle, the influence of the Membranes of 
Krause which constrict the nucleus along its length—and 
limit its ends—by their prolongation from the myofibrillae 
into the sarcoplasm. 
(3) The centrosome, which has been shown (in the 
resting cell) often to repel that part of the nuclear membrane 
which is nearest to it. 
(4) The relation between cell shape and nuclear 
shape has been briefly discussed. It has been noted that 
the nucleus never comes into contact with the 
cell membrane, except in the rarest instances due to the 
intervention of mechanical factors. Evidence has been brought 
forward in favour of our view that there is a mutual 
repulsion between cell membrane and nuclear 
membrane. 
(5) Canaliculi and incisions in the nuclear membrane 
have been described in various cells. 
(6) The unfolding of such incisions during development and 
differentiation of some such cells has been described. 
(7) Intranuclear rodlets and _ their importance in 
the maintenance or the modifying of nuclear shape have been 
discussed. 
(8) Mitotic division and a certain degree of nuclear 
differentiation have been shown often to be incompatible— 
thereby accounting for amitosis in certain highly specialized 
nuclei. 
(9) The need for care in distinguishing between nuclear 
incisions and genuine amitotic division of nuclei has been 
emphasized. 
June 1921. 
