164 
Proceedings of the Royal Society of Edinburgh. [Sess. 
and enlarged before atrophy and absorption take place. The cell membrane 
is indistinct, and the large nucleus appears in many places to be lying in a 
mass of granular cytoplasm or syncytium. As the ovary is examined from 
the periphery inwards, some cells in the fine spireme stage are seen, but this is 
a very transitory stage. The stage of the chromatin of the nucleus forming a 
reticulum— when the oocyte is first differentiated — is such a prolonged one 
that the chromatin filaments, becoming lengthened and gradually forming a 
spireme, can hardly be called a definite stage at any given moment. The 
chromatin spreads all over the nucleus as a fine filament, which becomes 
twisted into loops, as if wound round the nucleus like a spiral thread. At 
one side the threads seem to be more concentrated, and are gradually gathered 
into the skein close to the nuclear membrane. These fine filaments enter 
the skein in pairs, parallel rows, and loops ; they become enmeshed in the 
chromatin mass, and at a further stage the whole nucleus is clear, with the 
exception of one side where the chromatin threads are closely intertwined. 
The nuclear membrane is present, but is faintly stained, giving the cells the 
appearance of a granular mass of cytoplasm (syncytium) with small rounded 
cavities in its substance ; at the sides of the cavities are dark masses of 
chromatin. These are nuclei in the stage of synapsis. Fig. 8 shows an 
oocyte (a) with the chromatin distributed in the form of a reticulum and a 
well-marked nucleolus ; (b) shows the thin spireme stage, with knots of 
chromatin at the intersection of the filaments. No nucleolus is shown, but 
it is present in many cells, although faintly stained. In (c) the filaments 
are gathered to one side of the nucleus and the membrane is not well 
marked. The filaments are entering the skein in pairs. In (d) a further 
stage is seen, with greater complexity of the filaments ; ( e ) shows all the 
filaments in the mass, the loops appearing to be single and much thicker. 
The final stage of synapsis is seen in (/), where the loops of thick threads 
are becoming disentangled and spreading over the nucleus. These thick 
filaments have chromatin granules on their surface. These granules are also 
seen on the linin or achromatic threads, giving them a beaded appearance. 
This last figure shows the first stage of the thick spireme nucleus with 
single filaments (pachytenes). There is no evidence that the skein in the 
synaptic stage is always formed at a particular pole of the nucleus ; this is 
impossible to prove, owing to the varying directions in which the sections 
are cut. I could not find any evidence at this stage of an idiosome in the 
cytoplasm which might influence the position of the skein of filaments. 
Cells in the synaptic stage are seen in groups of four and five, and are 
deeper in the tissue of the ovary than the previous stages of oocyte develop- 
ment. 
