432, A. J. NICHOLSON 
not reasonable, therefore, to consider the yolk nucleus of 
Pholeus and the branching nucleus of A. maculipennis 
as being homologous structures which only differ in that the 
one passes to the outside of the nuclear membrane while the 
other remains inside ? 
I have already shown that the branching nucleus of the 
oocyte in A. maculipennis can only be regarded as 
a structure the function of which is to carry nutritive material 
to the various parts of the developing oocyte. After an 
exhaustive consideration of the various theories as to the func- 
tion of the yolk nucleus Bambeke comes to the conclusion that 
the only one which can be adopted in the case of Pholeus 
‘est celle qui considére ce corps comme centre de formation 
des éléments nutritifs du vitellus ’ 
Tor these reasons I have come to the conclusion already 
stated that the branching nucleus of Anopheles 
maculipennis and the yolk nucleus of Pholeus 
phalangioides are morphologically and physio- 
logically comparable. These structures are homologous 
with other types of oocyte nuclei and Corpuscles of Balbiani 
respectively. It would therefore appear that the Corpuseles of 
Balbiani may be considered as portions of the ooeyte nucleolus 
which have escaped through the nuclear membrane in order 
to carry on the nutritive portion of the nuclear functions. 
In Pholeus the division of the nucleus into two portions, 
ohe nutritive or vegetative and the other germinal, is only 
partial, as the germinal vesicle itself appears amoeboid and 
evidently takes part in the nutrition of the oocyte. 
In A. maculipennis it has been shown that from an 
early stage the nuclear contents are sharply divided into 
uw vegetative and a germinal portion, the nucleolus and 
chromatin residue respectively. During the resting stage there 
may be an apparent fusion of the two, but actually they are 
only closely applied together, the chromatin residue lying 
in an identation of the nucleolus. A close parallel is found in 
the ovary of the dragon fly according to McGill (19). In this 
case the thick spireme of the young oocyte surrounds the 
