428 A. J. NICHOLSON 
fixation, and in addition the branching has a definite spatial 
relation to other cell structures, yolk formation, and the 
position of the nucleus in the cell. The branched appearance 
of the nucleus is not confined to any type of section and it is 
a perfectly constant character in no way dependent on the 
fixative. Also it is not possible to regard the branches as 
the result of the pressure of the yolk-laden cytoplasm, so that 
the only possible explanation is that the oocyte nucleus of 
A. maculipennis is in a state of great activity during the 
period of yolk formation. 
It has been shown that the oocyte nucleus only commences 
to branch when the yolk begins to appear, and that when all 
the yolk has been produced and the nutrition of the oocyte is 
complete, the branching nucleus breaks down and its substance 
is absorbed directly by the cytoplasmic portion of the yolk- 
mass. Immediately before the final disappearance of the 
branching nucleus this structure rapidly loses its power of 
taking up stain. This is a further indication of the close 
similarity existing between the oocyte nucleus of A. maculi- 
pennis and the nuclei of secretory cells. Thus Bambeke (1), 
speaking of glandular cells, points out that after the secretion 
has lasted for a certain time the power of the nucleus to take 
up nuclear stains diminishes. 
At this point it will be convenient to examine some of the 
various mechanisms which have for their object the nutrition 
of the rapidly-growing oocyte. In each case it will be found 
that the main object of the mechanism is to increase the surface 
in contact with the evtoplasm of the oocyte, in order to facilitate 
the passage of nutritive material into the latter. 
The activities of the oocyte nucleus in Colymbetes 
fuscus as described by Will (84) are in many ways not unlike 
those of the insect under consideration. When the oocyte 
enters on its period of rapid growth the nuclear membrane 
becomes irregular and finally many small branches pass into 
the cytoplasm. Later these become separated from the rest 
of the nucleus, and are used directly as nutritive material by 
the cytoplasm. A fresh nuclear membrane develops behind 
