160 
Proceedings of the Royal Society of Edinburgh. [Sess. 
defined nucleolus and marked chromatin filaments scattered irregularly 
through the nucleus. These are the oocytes of the first order, or deuto- 
broque cells. Mitosis is seen among these cells. The stroma cells are be- 
ginning to push up through the germ cells, which in their turn burrow 
downwards, and thus egg clusters or nests are formed. 
Embryo 10 cm. — The layer of oogonia is diminishing in breadth at the 
periphery, owing to the advance of the egg clusters. The stroma cells are 
pushing upwards and the central ends of the egg columns are rounded in 
outline. In the deeper portions of the nests are numerous oocytes of the 
first order, with a definite nucleolus and well-marked chromatin filaments. 
In addition to these are larger cells, where the filaments become lengthened 
and spread out over the nucleus ; these filaments are in the form of very 
fine threads, and in the larger cells they are seen to be spread over the 
whole nucleus in the form of a spireme (noyaux leptotenes). The first stage 
of the oocyte may be called “ the resting stage,” and there are several 
transitional stages between it and the fine spireme stage, the latter being of 
extremely short duration. Like other observers, I cannot make out whether 
the filament is a single long cord cut in several lengths by the microtome, 
or numerous filaments from the beginning. 
Embryo 12 cm. (fig. 1). — The cortical and medullary zones are well 
marked. The ovary is kidney-shape in outline. The cell nests are nearer 
the surface, very large nests being seen in the outer layers and smaller in 
the more central portions. In the medullary zone are large blood spaces. 
In the cell nests are masses of cytoplasm with irregularly distributed 
nuclei — the “ syncytial masses ” ; some of the nuclei in these masses show 
signs of degeneration, and vacuoles are seen in the cytoplasm itself. The 
resting oocytes are in great numbers in the peripheral cell nests, and in the 
deeper are the transitional cells and spireme stage cells. In addition are 
cells with nuclei in synapsis, where the chromatin filaments are drawn to one 
side of the nucleus, and also transitional stages between these nuclei. The 
rest of the ovarian structure is made up of stroma cells and oogonia which 
have not become differentiated into oocytes. These cells are numerous 
under the capsular layer and at the medullary portion of the cell nests. 
Some of these cells are beginning to form round the larger cells — the early 
appearance of the primitive or primordial follicle. The medullary cords 
are not well marked, but some rows of small cells can be made out in the 
neighbourhood of the hilum ; these show degenerative changes in their 
substance. 
Embryo 14 cm . — The stroma cells have approached nearer to the 
periphery, and the layer of oogonia are therefore reduced in number. 
