1910-11.] Development of Germ Cells in Mammalian Ovary. 155 
poussieroides. The nucleolus is more marked in the kitten’s germ cells 
than in those of the rabbit. 
Miss Lane-Claypon agrees with the work of v. Winiwarter in the main 
points, although she finds little evidence of a differentiation between the 
cells of the protobroque a and b varieties. Mitosis is found in the deuto- 
broque cells for the most part. The oogonia form the follicle cells around 
the oocyte, their numbers being increased by the streaming in of others 
from the periphery. Some of the oogonia do not form follicle cells, but go 
to the formation of interstitial cells, which are metamorphosed deutobroque 
cells. The stroma cells only function as supporting and vascular. Bryce 
describes the nuclear changes in three phases, — a pre-reduction phase, which 
includes all generations up to that of spermatogonia or oogonia, the nuclei 
having the same number of chromosomes as the somatic nuclei. A reduc- 
tion phase, which involves the generations, however, as spermatocytes, and 
oocytes of the first and second orders, and which have two divisions, during 
which the number of chromosomes is reduced to one-half that of the somatic 
number. The first division is called heterotypical, the second homotypical 
division. The post-reduction phase is the mature sex cell, and ends at its 
fertilisation, when the somatic number of chromosomes is restored in the seg- 
mentation nucleus formed by the union of the germ and sperm cells. The 
prophase of the first or heterotypical division is very prolonged. 
A parallel process in the microsporcytes of plants is given by Jules 
Berghs (2), who shows that the chromatin filaments are in pairs in the 
synaptic stage. In his figures the nucleus is shown in different stages, 
the apparent reduction taking place in the synaptic stage ; the true 
reduction only takes place by the separation of the daughter chromo- 
somes towards the two poles of the first mitosis. Lerat (14) also gives a 
detailed account of the behaviour of the chromosomes in Cyclops strenuus, 
where are seen large cells with a nucleus four or five times greater than 
the others, being cells in all probability in repose. The skein in the synaptic 
stage is formed of numerous filaments, no centrosome being found which 
would influence the position of the chromatin mass. Two types of the 
synaptic stage are seen — the fine and thick filaments. The thick fila- 
ments split longitudinally, reduction during synapsis being only a pseudo - 
reduction. The nucleolus is present throughout all the nuclear changes, but 
stains faintly in some stages. At the stage of maturation the nucleolus 
exchanges chromation with the chromosomes, but not relationships ; there 
is a “ distinction parfaite entre le nucleole et les chromosomes.” In the zone 
of multiplication mitosis takes place with the normal number of chromo- 
somes, and therefore numerical reduction does not precede the first mitosis 
