SHAPE OF THE NUCLEUS 591 
It is a curious fact that such nuclei usually contain a single 
nucleolus only, and that this body tends to be in the centre of 
the nucleus or somewhat deviated towards that pole of it which 
is farthest from the centrosome. The latter seems to exercise 
a repellant action on the nucleus also—a fact which can be 
verified in many cells with large nuclei, e.g. spermatocytes. 
Lobulation of the nucleus can sometimes be attri- 
buted to variations in surface tension at the interfaces of 
TEXT-FIG. 1. 
Phagocytic cell (amoebocyte) from a larva of Phr yganea sp.— 
a caddis fly. Extreme polymorphism of the nucleus probably 
due to variations in surface tension over the nuclear membrane. 
Nu, nucleolus; va, vacuole. Technique: Bouin and _ iron 
haematoxylin. 
nucleus and cytoplasm. A striking example of this is furnished 
by the large cells accompanying histolysis during metamor- 
phosis in insects. Here, as is well known, the larval tissues 
are destroyed by large phagocytic cells known as Amoebocytes. 
Text-fig. 1 shows such an element from a larva of Phr yganea 
sp. Here the polymorphism of the nucleus is extreme, while 
the nucleolus, which is single and central, does not appear to 
be involved in the lobulation. Of the latter, every degree 
RY 2 
