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Transactions of the Society. 
been such as to enable me to identify it before this stage, although 
it may possibly be derived from the nucleolus after its reduction 
in size. In Ranatra Chickering finds in the first type twenty-one 
chromosomes, all of which divide equally in the primary division, 
whilst in the secondary there are twenty-one again, but two do not 
divide, passing into different spermatids, so that each posseses 
twenty chromosomes. These are described as the typical 
XY-group, but owing to their behaviour, their identification is 
not possible before this stage. In the second type no numbers 
are given nor X and Y chromosomes described, the only note 
being a reference to a group of small chromosomes near the centre 
of a larger group, which seems to be a distinguishing feature, but 
nothing corresponding to this has been found in Nejpa. An ex- 
amination of the equatorial plates of the primary division gives 
further evidence in favour of the fact that the X-chromosome 
passes over in the first division. It was found that approximately 
half the counts gave seventeen and the other half eighteen in the 
same group of cells. The chromosomes varied in size, there being 
nothing conspicuous, and on close examination and comparison 
they were found to practically correspond in size except for one 
of the larger members. In Notonecta there is an XY-group which 
apparently divides equationally in the first division, but they 
separate in the second. 
The preparations of the oogonia covered all the stages up to 
the growth stage of the egg. Oogonial mitoses were not so frequent 
as those in the spermatogonia, but sufficient numbers were studied 
to enable satisfactory counts to be made. They resulted in thirty- 
six being the diploid complex, so that the unpaired element of 
the male germ cells is accompanied by a homologous partner. 
Here again the chromosomes varied, but there were no outstanding 
members. The nuclear figures accompanying the maturation stages 
were essentially identical with those phenomena of the spermato- 
cytes as far as the diplotene, the nucleolus being as before very 
prominent. At this stage differentiation into follicle and nurse 
cells and oocytes took place. In the latter case the threads 
remain, but gradually disappear as the nucleolus increases in size 
and the cell moves towards the neck of the nutritive chamber. 
EXPLANATION OF PLATE XI. 
Fig. 8 a . — Maturation stages of male. Diplotene showing ring formations. 
Fig. 9. — Spindle of first division showing unpaired chromosome. 
Fig. 10. — Equatorial plate of second spermatocyte, 17 chromosomes. 
Fig. 11. — Equatorial plate of second spermatocyte, 18 chromosomes. 
Fig. 12. — Anaphase stage of division showing X in front of autosomes. 
Fig. 13. — Anaphase stage of division showing X behind autosomes. 
Fig. 14. — Ejection of particles from nucleus showing others in cytoplasm. 
Fig. 15. — Resting stage of egg showing yolk particles at border of egg follicle 
cells, and diffuse stage of nuoleus. 
