1910-11.] Development of Germ Cells in Mammalian Ovary. 173 
owing to the density of the skein. After emergence from the skein the 
filaments become spread over the nucleus and form a spiral — the thick 
spireme stage. This is also prolonged. During all these stages the nucleus 
is increasing in size and the cytoplasm becoming more abundant. In the 
next stage, that of the double filament stage, the thick rods are divided 
longitudinally and have the appearance of parallel pairs. This division is 
only apparent, as complete fusion has not been present (pseudo-reduction of 
the chromosomes). These filaments separate, some forming loops and rings. 
Transverse segmentation takes place, and the short filaments form figures of 
eight rings and short rods. This is the resting stage or germinal vesicle. 
It may last for years, and in the human ovary is very prolonged. The 
chromatin becomes broken up and the cytoplasm vacuolated. These 
chromatin filaments become more definite when the oocyte is ready for 
fertilisation at the time of the formation of the polar bodies. The nucleolus 
in the resting stage is well defined — the germinal vesicle ; and the large 
amount of deutoplasm is the food for the future growing embryo. The 
cells of the ovary develop from the periphery inwards, the younger cells 
being near the surface. The stages of the cell development here described 
belong to the prophase of the heterotypical division. Reduction of the 
filaments is a temporary and only apparent process, as true reduction to 
half the number of somatic chromosomes does not take place until a late 
stage, i.e. after extrusion of the oocyte from the ovary, when it is termed an 
oocyte of the second order. 
Multiplication by mitosis ceases at a given time, and in the human 
ovary the formation of the final stages of the oocytes of the first order is 
completed before or just after birth. 
[Diagram. 
